Click here to watch a video showing a patient before and after receiving the subthalamic nucleus deep brain stimulation for Parkinson’s disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder that initially affects the dopaminergic system and eventually involves other neurotransmitter systems, with an unrelenting course. It is well known that motor fluctuations like wearing-off and peak-dose dyskinesia are common motor complications few years after patients are started on medical treatment. When these complications become very disabling despite maximal adjustment of pharmacological agents, deep brain stimulation (DBS) has been shown to be effective and safe with lasting benefits for at least up to 10 years.1 2 3 4 5 Deep brain stimulation is a neurosurgical intervention that entails inserting microelectrodes with imaging and neurophysiological guidance at targeted regions, such as the subthalamic nucleus (STN) or globus pallidus interna (GPi) in order to achieve alleviation of most of the motor complications. We studied DBS performed in a cohort of PD patients in a single Hong Kong centre over a period of 12 years. Patients’ outcomes improved significantly throughout all these years. Here, we review our results of STN DBS for PD and summarise our experience, with particular emphasis on evaluating the effectiveness and safety of this novel treatment.

Patients who fulfilled the Queen Square Brain Bank Criteria for diagnosis of PD and experienced significant disability due to motor fluctuations despite maximal medical therapy were admitted to the Prince of Wales Hospital and jointly evaluated for the suitability for DBS by a Movement Disorder Group composed of neurologists, neurosurgeons, and a nurse specialist. After June 2005, this multidisciplinary group was further developed to include a radiologist, clinical psychologist, occupational therapist, physiotherapist, and speech therapist. The assessment comprised a predefined protocol, which was continuously updated over the years. This assessment protocol included clinical assessment, levodopa challenge test, video recording, neuroimaging, and neurocognitive and psychiatric evaluations. Patients who received STN DBS from September 1998 (the first patient who received STN DBS in our centre) to January 2010 were included in the present study. Assessment data were obtained before and after the operation (medication-off state and stimulator-on) and included the Unified Parkinson’s Disease Rating Scale (UPDRS), modified Hoehn-and-Yahr stage (both at PD off-state), levodopa equivalent dose, body weight, and patients’ diaries at preoperation and at least 2 months postoperation.

All patients had stereotactic guidance for the insertion of electrodes under local anaesthesia. Microelectrode recording (MER) technique was introduced since year 2000. Frame-based stereotaxy was performed in most of the patients except three who underwent frameless stereotaxy (2005) with equally accurate targeting. Before 2003, an old version of Zeppelin magnetic resonance imaging (MRI)–compatible frame was used, which was not compatible with the computer planning system available at that time. Since 2003, a Leksell G frame (Elekta AB, Stockholm, Sweden) was acquired together with a computer planning system (iPlan; Brain LAB, Feldkirchen, Germany) for image targeting and trajectory planning. With these, the image targeting and trajectory were planned based on preoperative MRI. On the day of operation, a computed tomography (CT) scan of brain with the stereotactic frame fixed to the head was performed and fused to the MRI plan in the computer planning system. Such a practice gave us more time for image targeting and shortened the time used for MRI and target planning on the day of operation before entering the operating theatre; this contributed to the accuracy of STN targeting and patient comfort. A dedicated MRI protocol was established since 2008, which ensured the consistency of high-quality MRI for targeting. In 2003, microdriver was introduced for MER which provided sub-millimetre advancement of the microelectrode to obtain more details of neuronal discharges and, thus, better quality of MER for neurophysiological targeting. Macrostimulation was performed in all patients for target confirmation. Deep brain stimulation electrode was implanted if satisfactory signals from MER and response from macrostimulation were obtained. For anchoring the DBS lead at the burr-hole site, a reliable device (Navigus; Medtronic, Minneapolis [MN], US) was introduced in 2002. The Pulse Generator (Itrel II or Soletra for unilateral, Kinetra for bilateral; Medtronic, Minneapolis [MN], US) was implanted under general anaesthesia. The DBS was usually switched on within 2 weeks after the operation. A nurse specialist took up DBS programming under the supervision of a neurologist and neurosurgeon in 2004, which facilitated experience accumulation and consistency in DBS programming.

Descriptive data were expressed as mean ± standard deviation (SD). Wilcoxon test was used to compare scores of modified Hoehn-and-Yahr stage, levodopa equivalent dose, body weight, patients’ diaries, as well as scores of individual items of activities of daily living (part II) and motor examination (part III) of UPDRS before and after operation. Tests with a P value of ≤0.05 were considered to be statistically significant. Statistical analyses were performed with the Statistical Package for the Social Sciences (Windows version 15.0; SPSS Inc, Chicago [IL], US).

Between September 1998 and January 2010, a total of 51 PD patients received DBS. Of them, six received unilateral STN DBS, two received GPi DBS, and two received nucleus ventralis intermedius (VIM) stimulation. Overall, 41 patients received bilateral STN DBS (21 male, 20 female; age at operation: mean 54, SD 7, range 40-71 years). All were Han Chinese except one who was of Portuguese ethnicity. Mean (± SD) duration of PD at operation was 10 ± 4 (range, 3-22) years (Table 1).

There were three complications, namely, lead migration, infection, and cerebral haematoma; all occurred in 2001. Lead migration occurred in 2001 three months after the operation. The patient complained of increased PD symptoms after a fall on level ground. One DBS lead was found withdrawn from the target. It was related to the insecurity of lead fixation. Revision operation was done for the case with good recovery. Infection occurred in a case 3 weeks after DBS operation in 2001. Apart from abscess formation in the chest wall where the pulse generator was implanted, MRI brain showed contrast enhancement around the DBS electrodes. All the hardware including the pulse generator and the DBS leads were removed and the patient received a course of antibiotics. He received DBS again in 2006 and enjoyed good effect. Cerebral haematoma also occurred in 2001. The patient became drowsy during the operation. The surgery was stopped and CT brain revealed a subcortical haematoma likely related to venous infarction. Craniotomy for haematoma evacuation was performed. The patient recovered but with residual hemiparesis. There was no mortality.

At postoperative follow-up with a median assessment time of 12 months, both UPDRS parts II and III showed improvements of 32.5% and 31.5%, respectively (P<0.001) in the whole study sample (Table 2). In view of the evolvement of the protocol, improvement in targeting methods, refinement of surgical technique as well as accumulation of programming experience over the 12 years, the improvement rates in patients who had DBS from 1999 to May 2005 and from June 2005 to 2010 were analysed separately and compared. Patients in the later group had significantly higher rate of improvement than those in the early group (Table 3). The improvement in UPDRS part II and part III for the two groups were 5.1% vs 55.0% (P=0.005) and 13.2% vs 55.2%, respectively (P<0.001). The Figure shows the percentage of improvement in UPDRS parts II and III. There was statistically significant increase in body weight after operation as shown in Table 2. However, there was a non-significant trend with regard to the reduction of levodopa-equivalent daily dose after surgery. A comprehensive neurocognitive evaluation was established after 2008 (Table 4). Three patients completed pre- and post-operative evaluation. Their functioning level in various domains remained unaffected at postoperative evaluation, although a reduction in verbal fluency was noted. No separate statistical analysis was performed due to the limited number of subjects.

As per the patients’ own diary reporting, there were statistically significant improvements in “on-period without dyskinesia” (ie more ‘good-on’), “on-period with dyskinesia”, and “off-period” in terms of percentage of waking hours (Table 2).

Parkinson’s disease is a neurodegenerative condition typically manifesting in an unrelenting progressive course. Patients often show dramatic response to pharmacological treatments initially, but with time, motor complications like motor fluctuations with wearing-off or peak-dose dyskinesia occur, eventually leading to progressive disability. Deep brain stimulation has evolved as an important and established treatment option for advanced PD. The mechanism of DBS is generally believed to modulate the circuit function by inhibition or excitation through controlled electrical stimulation of different targets along the circuit. Subthalamic nucleus is the most often used target for PD. The benefits of DBS compared with ablative surgery include its non-destructive nature, reversibility, and adjustability. The procedure is mainly indicated for PD patients who are dopamine-responsive but with disabling motor complications such as motor fluctuation, dyskinesia, or intolerable side-effects of anti-PD medications.6 To date, there are controversies regarding the use of DBS in the early stage of PD, and most centres will offer this treatment for patients with significant motor complications refractory to maximal drug treatment. Convincing evidence shows that DBS is an effective treatment for PD patients and the benefits may last for at least 10 years.

Our study attempted to investigate the effectiveness and safety of bilateral STN DBS in PD patients who had disabilities refractory to best-available medical treatment. The study extends over a period of 10 years, trying to evaluate PD patients who received bilateral STN DBS. The study excluded patients receiving unilateral STN, as well as VIM or GPi DBS, so that the patient group was more homogeneous in the surgical therapeutic sense.

The median timing of postoperative assessment was 12 months (range, 2-77 months), and it demonstrated significant improvement in almost all parameters in UPDRS part II and part III, except for speech. Although our assessments were not performed at the same time intervals for all patients postoperatively, the results are still in concordance with findings in published studies evaluating efficacy of DBS at 6 months and 5 years postoperatively. Speech was also reported to be the only dysfunction that did not improve with STN DBS in published cohorts in general. The exact reason for this finding is yet to be unfolded; a recent paper suggested that speech impairment may be related to unintended activation of dorsal premotor cortex during STN stimulation,7 but it echoes with the observation that DBS improves symptoms which respond to levodopa; speech is, however, not one of those.

The UPDRS part II on activities of daily living indicated significant improvement, in terms of total rating, writing, and freezing of gait. Apart from objective assessment, patients’ self-evaluation from their own PD diary also revealed improvements in terms of more ‘good-on’ state, mobile without disabling dyskinesia, as well as less off-period compared with those after DBS.

Since our first case of DBS for PD in 1998, a multidisciplinary team comprising a neurologist, neurosurgeon, nurse specialist, radiologist, clinical psychologist, occupational therapist, physiotherapist, and speech therapist was gradually built up. From 2000 to 2004, important evolvement of our DBS protocol included: a monthly Combined Movement Disorders outpatient clinic run by a neurologist, neurosurgeon, and nurse specialist; regular case conference; dopamine challenge test; MER; acquirement of a stereotactic frame together with a computer planning system for imaging targeting and trajectory planning; and appointment of a dedicated person for DBS programming. Our experience also increased considerably in the areas of systematic auditing of targeting accuracy, surgical complications, and clinical outcome.5 All these serve to explain the significant improvements in the outcomes after 2005 as shown in the Figure. Our current DBS protocol since 2009 for PD is shown in Table 4.

We found a non-significant trend in reduction in the dose of anti-Parkinsonian medications in terms of levodopa-equivalent medications after STN DBS. This possible reduction in medication usage is a common finding in previously published reports3 and indicates increased independence from pharmacological treatment after the surgery. We also showed that weight gain was significant after STN DBS, which is consistent with findings in the current literature. There have been plenty of studies looking into the possible mechanisms,8 but the exact causes remain uncertain. Preliminary data show that weight gain might even be more commonly encountered in STN as compared with GPi DBS in PD, suggesting additional factors in STN stimulation.9

The complication rate in our study is comparable with that in another DBS centre with 8.6% hardware-related complication.10

There are limitations in our study. This was not a prospective study. Although the data were collected prospectively, the protocol itself was continuously evolved. Our patients were not assessed uniformly at the exact same time-points postoperatively; the timing of postoperative evaluation ranged from 2 months to 77 months (mean ± SD, 17.0 ± 15.4 months), which is a rather wide range. This was related to the logistic arrangements for patients to have overnight admission for ensuring 12 hours off-medication and availability of beds in a busy tertiary emergency hospital. Quality of life (eg 39-item Parkinson’s disease questionnaire) is an important component of outcome assessment but it was not used in this cohort. There was no systematic neuropsychology assessment until 2008. Despite all these shortcomings, our study is the first series in Hong Kong reporting the treatment outcomes as well as the experience gained over 12 years in bilateral STN DBS for PD patients.

Bilateral STN DBS for PD patients having motor disabilities refractory to medical treatment showed significant improvement in motor performance and functional state, except for speech, during an observation period of up to 77 months. The surgical procedure was shown to be safe, with no perioperative mortality. Patients were found to consume less anti-Parkinsonian medications and reported less dyskinesia, but had increased body weight. A dedicated multidisciplinary team building, refinement of protocol for patient assessment and selection, improvement of targeting methods, meticulous surgical technique, and experience in programming are the key factors that contributed to the improved outcomes.

1. Chan DT, Mok VC, Poon WS, Hung KN, Zhu XL. Surgical management of Parkinson’s disease: a critical review. Hong Kong Med J 2001;7:34-9.

2. Moro E, Lozano AM, Pollak P, et al. Long-term results of a multicenter study on subthalamic and pallidal stimulation in Parkinson’s disease. Mov Disord 2010;25:578-86. CrossRef

3. Schüpbach WM, Chastan N, Welter ML, et al. Stimulation of the subthalamic nucleus in Parkinson’s disease: a 5 year follow up. J Neurol Neurosurg Psychiatry 2005;76:1640-4. CrossRef

4. Krack P, Batir A, Van Blercom N, et al. Five-year follow-up of bilateral stimulation of the subthalamic nucleus in advanced Parkinson’s disease. N Engl J Med 2003;349:1925-34. CrossRef

5. Chan DT, Zhu XL, Yeung JH, et al. Complications of deep brain stimulation: a collective review. Asian J Surg 2009;32:258-63. CrossRef

6. Zhou JY, Yu Y, Zhu XL, Ng CP, Lu G, Poon WS. Parkinson’s disease: insights from the laboratory and clinical therapeutics. In: Nagata T, editor. Senescence. InTech 2012; 587-616. CrossRef

7. Narayana S, Jacks A, Robin DA, et al. A noninvasive imaging approach to understanding speech changes following deep brain stimulation in Parkinson’s disease. Am J Speech Lang Pathol 2009;18:146-61. CrossRef

8. Montaurier C, Morio B, Bannier S, et al. Mechanisms of body weight gain in patients with Parkinson’s disease after subthalamic stimulation. Brain 2007;130:1808-18. CrossRef

9. Sauleau P, Leray E, Rouaud T, et al. Comparison of weight gain and energy intake after subthalamic versus pallidal stimulation in Parkinson’s disease. Mov Disord 2009;24:2149-55. CrossRef

10. Baizabal Carvallo JF, Mostile G, Almaguer M, Davidson A, Simpson R, Jankovic J. Deep brain stimulation hardware complications in patients with movement disorders: risk factors and clinical correlations. Stereotact Funct Neurosurg 2012;90:300-6. CrossRef

Acute respiratory distress syndrome (ARDS), after severe viral or bacterial infection, is a common cause of severe respiratory failure in the Intensive Care Unit (ICU). The syndrome is defined as acute onset of hypoxaemic respiratory failure, which is accompanied by bilateral infiltrates of chest, and occurs due to non-cardiogenic cause.1 2 Despite vigorous researches on pharmacological treatment and ventilator strategy in recent decades, ARDS with profound hypoxaemia continues to be associated with high mortality rate. In 2009, the conventional ventilatory support versus extracorporeal membrane oxygenation (ECMO) for severe adult respiratory failure (CESAR) trial, conducted by Peek et al3 in the UK, showed a significant survival advantage with the use of ECMO for patients with severe ARDS. Extracorporeal membrane oxygenation is a life-support technology with a history of more than 40 years.4 With the evolution of technology, the procedure has become simpler, safer, and more reliable. Since 2010, the Queen Elizabeth Hospital (QEH) in Hong Kong has started providing venovenous (v-v) ECMO to selected patients with severe respiratory failure due to severe ARDS and profound hypoxaemia.

This was a retrospective observational study performed in a 19-bed ICU of a tertiary hospital in Hong Kong. Eligible patients needed to have potentially reversible causes for respiratory failure, refractory respiratory failure despite maximum conventional ventilator support, and Murray score of 3.0 or higher (Murray score4 is calculated by: PaO₂/FiO₂ ratio, positive end-expiratory pressure [PEEP], lung compliance, chest radiographic appearance). Patients with acute-status asthmaticus and refractory respiratory failure were also selected as candidates for ECMO despite having Murray score of lower than 3.0. Patients were excluded for ECMO therapy if they had intracranial bleeding; severe, irreversible brain damage; or were older than 70 years.

The QEH ECMO team supports eligible patients from other ICUs that do not have ECMO service. The QEH ECMO retrieval team puts eligible patients in the referring hospitals on ECMO circuit, and then escorts them to QEH. The team consists of two intensivists and two intensive care nurses.

Access catheters (Maquet HLS, Germany; BIOLINE coating) were inserted in either the right or left femoral vein, and return catheters were inserted in the right internal jugular vein. All cannulation procedures were performed at the bedside, by ICU specialists, with Seldinger technique and ultrasound guidance. The size of the cannulas was chosen according to the body weight of patients. The default size was 19 Fr for return catheter and 23 Fr for access catheter. The jugular-femoral approach for return (19 Fr) and access (23 Fr) catheter cannulation was adopted for all patients. The catheters were connected to the ECMO machine (either Rotaflow: BE-PLS 12050–Quadrox PLS [Jostra], or Cardiohelp: HLS module advanced 7.0).

As per our ICU ECMO protocol, ECMO nurses and ECMO specialists have to provide special regular monitoring of coagulation status, circuit conditions, perfusion status, and neurological status. Accordingly, unfractionated heparin infusion is the default and only anticoagulant used. Anticoagulation is monitored at the bedside with a target-activated clotting time of 180-220 seconds. Activated clotting time is measured every 4 hours. We maintain a platelet count of 100 x 10⁹ /L, international normalised ratio of <1.5, and haemoglobin level of >120 g/L. The ECMO nurses need to check the following every 4 hours: presence of clot in the oxygenator membrane, any colour difference between the access and return catheters, and oxygenator membrane pressure gradient. The post-oxygenator partial pressure of oxygen and free-haemoglobin level are checked daily.

We use benzodiazepine and narcotics for sedation. Pupil size, sedation score, and conscious status are assessed every 4 hours. Propofol is not recommended due to the potential interaction with oxygenator membrane. Enteral nutrition is used when possible, and as early as possible, according to our ICU feeding protocol. Fluid balance is maintained with diuretics and continuous v-v haemofiltration, as clinically indicated.

Once the ECMO support is started, we change the ventilator setting so as to allow ‘lung rest’ (ie FiO₂ 0.4, PEEP 10 cm H₂O, tidal volume 4 mL/kg, rate 10 cycles/min) with an inspiratory/expiratory ratio of 1:1.3.

Continuous v-v haemofiltration is used for patients with acute kidney injury, excessive fluid gain, and metabolic acidosis. The venous and arterial lines are connected at post-pump to minimise the risk of air embolism.

Heparin infusion is stopped 30 minutes before decannulation. Decannulation is performed at the bedside with two-team approach. Both jugular and femoral catheters are removed simultaneously. Direct pressure is then applied to the sites for at least 15 minutes.

Normally distributed data were expressed as mean ± standard deviation (SD). Independent t test was used for comparison of means. Data, if not normally distributed, were expressed as median and interquartile range (IQR). Mann Whitney U test was used for comparison of medians. Categorical data were analysed using Fisher’s exact test. Statistical analysis was performed using the Statistical Package for the Social Sciences (Windows version 17; SPSS Inc, Chicago [IL], US). P values of <0.05 were considered statistically significant.

This proposal was reviewed and approved by the Research Ethics Committee of the Kowloon Central Cluster/Kowloon East Cluster (Kowloon Central/ Kowloon East; REC [KC/KE]).

Between 1 July 2010 and 30 June 2013, 31 patients (mean ± SD, 42.2 ± 14.1 years; 21 males) received v-v ECMO for the treatment of severe respiratory failure and ARDS. The median body mass index was 22.6 (IQR, 21.5-24.8) kg/m². The median Murray score was 3.5 (IQR, 3.0-3.5). A total of 11 cases were retrieved from other acute hospitals. The median time required for patients to arrive at the ICU was 7.0 (IQR, 3.0-8.0) days (Table 1). The mean duration of mechanical ventilation before starting ECMO treatment was 1.6 ± 2.7 days.

Male gender and younger age were associated with better survival rate, although they did not attain statistical significance. Survivors and non-survivors had similar Murray scores. Survivors had a higher pre-ECMO PaO₂/FiO₂ ratio, lower APACHE (Acute Physiology And Chronic Health Evaluation) II and APACHE IV scores, and shorter time for symptoms to ICU admission versus the non-survivors, but none of the differences was statistically significant (Table 1). Of the 31 patients who presented with respiratory failure, 28 (90.3%) were diagnosed to have pneumonia, one had severe smoke inhalation injury, and two had status asthmaticus; 22 of the 28 pneumonia patients had identifiable laboratory causes (Table 2). Patients suffering from viral infection as primary cause of respiratory failure (1 dead/11 alive) had better ICU survival than those suffering from bacterial infection (2 dead/8 alive); however, the difference was not statistically significant (92% vs 80%, P=0.57, Fisher’s exact test; Table 2). Overall, nine (29.0%) patients were diagnosed to have H1N1 infection, either by polymerase chain reaction or serology or both. Patients with H1N1 as the cause of respiratory failure had excellent survival outcome (100%; Table 3).

The median (IQR) duration of ECMO therapy was 5.0 (2.8-8.6) days. The median length of ICU stay was 18.0 (11.6-25.8) days, and median length of hospital stay was 23.5 (15.3-40.9) days. A total of 25 (80.6%) patients survived ICU discharge and 24 (77.4%) patients survived hospital discharge and had 28-day survival (Table 4).

On logistic regression analysis, APACHE II score was the only significant factor that could predict hospital mortality.

Of the 31 patients, two (6.5%) patients developed severe haemorrhage (haemothorax [n=1] and cerebral bleeding [n=1]) and three (9.7%) patients developed mechanical complications of the circuits (clotted membrane [n=1], suspected oxygenator failure [n=1], and vascular injury [n=1]).

The first successful ECMO treatment case was reported in 1972.5 However, two randomised controlled trials6 7 that were published several years after this reported case failed to show any significant advantage with ECMO. The use of ECMO in adult patients remained limited until publication of the CESAR trial in 2009,3 which showed significant advantages with ECMO in terms of survival for patients with severe respiratory failure and ARDS after H1N1 pandemic.

Our patients, who were managed with v-v ECMO for severe respiratory failure, had ICU mortality and hospital mortality of 19.4% and 22.6%, respectively. Most of them (n=29; 93.6%) had severe ARDS that failed conventional treatment. Our results (7 dead/24 alive) compared favourably with the ECLS (Extracorporeal Life Support) Registry Report,8 in which the hospital mortality was reported to be 44% (2283 dead/2905 alive; P=0.018 by Fisher’s exact test). Mortality of ARDS, before 1990s, was higher than 50%.9 10 Mechanical ventilator is the cornerstone of treatment for ARDS. Although it can support lung ventilation, inappropriate use can lead to lung damage including excessive transpulmonary pressure (barotrauma), excessive lung volume inside alveoli (volutrauma), and shearing stress during repetitive opening and closing of alveoli (atelectrauma).11 Moreover, the damage caused by mechanical ventilation is not limited to the lungs. Lung trauma can trigger systemic inflammatory response (biotrauma) that involves other distal organs leading to multiorgan damage. To date, the only strategy that can improve survival is lung protective strategy (≤6 mL/kg of predicted body weight; plateau pressure ≤30 cm H₂O).12 13 With the use of lung protective strategy and ECMO treatment, recent publications reported a mortality of approximately 20% to 40%.3 14 Lung protective strategy was the most evidence-based approach in ARDS management. Extracorporeal membrane oxygenation use in ARDS patients can ensure the effective application of low tidal volume and plateau pressure strategy.

In our report, the mean tidal volume after ECMO therapy was 288.0 ± 76.8 mL, which was within the higher limit of the expected tidal volume (390 mL) according to the lung protective strategy (Table 1). The ICU mortality and hospital mortality rates in our cases were 19.4% and 22.6%, respectively. These figures are favourable when compared with patients who receive only lung protective strategy.13 In fact, ICU doctors often face challenges to comply with the lung protective strategy in real situation. The presence of stiff lung and hypercarbia in severe ARDS patients may make it difficult for ICU doctors to set low tidal volume and transpulmonary pressure. The use of ECMO, however, can overcome these challenges. Extracorporeal membrane oxygenation can allow both CO₂ removal and oxygenation with an independent circuit that bypasses the sick lungs. This permits complete lung rest with the lung protective strategy.

H1N1 infection is widely reported to have better survival rate and shorter duration of ECMO support, mechanical ventilator days, and length of ICU stay. According to the ELSO (Extracorporeal Life Support Organization) registry (as dated to 13 April 2011), the H1N1 survival rate was 76.8% (66 dead/218 alive) in patients older than 20 years.15 In our study, all nine H1N1 swine flu patients survived (Table 2). H1N1 patients in Hong Kong had more favourable outcomes compared with those in Australia and Canada (Table 3).14 16 17 These outcomes included shorter ECMO duration, shorter ventilator days, and shorter ICU and hospital length of stay. Future study shall explore other factors that affect outcomes including duration of inter-hospital transportation, manpower availability, and use of pharmacological treatment. In our centre, all H1N1 patients received N-acetylcysteine (NAC) intravenous infusion together with oseltamivir from day 0 of ICU admission. The effect of NAC, an antioxidant18 19 20 21 as adjunct therapy in treating severe H1N1 respiratory infection, deserves further exploration in future.

In our study, vascular injury was the single complication that was related to the procedure. We encountered one oxygenator-related thrombosis and one suspected oxygenator failure. In one case, we postulated that the cause of thrombosis was hypercoagulopathy related to mycoplasma infection. Another case had contra-indication to heparin due to active bleeding. One patient was diagnosed with intracerebral bleeding after initiation of ECMO therapy. The bleeding was probably related to the patient’s own brain pathology. The patient was diagnosed with haematological lymphoproliferative disease that probably infiltrated the brain and caused death, as suggested by the postmortem examination.

Our report had several limitations. As ECMO therapy is relatively new in our centre, we have a limited number of cases. This study was a retrospective review of a single-centre experience. All patients who received ECMO therapy were carefully selected, and we did not have a control group to demonstrate the superiority of ECMO therapy. We only considered mortality as our main outcome and did not follow-up the long-term morbidity of the survivors. Future study with ECMO shall consider outcomes that cover physical, functional, and neuropsychological aspects.

Venovenous ECMO is an effective adjunctive therapy, useful as a life-saving procedure for carefully selected severe ARDS patients when the limits of standard therapy have been reached.

Soft tissue tumours represent a diverse group of mesenchymal lesions which often present diagnostic challenges to clinicians and pathologists. Histological classification of these tumours is based on their degree of differentiation and metastatic potential: benign, intermediate (locally aggressive), intermediate (rarely metastasising), and malignant.1 Recent advances in molecular cytogenetics (fluorescence in-situ hybridisation [FISH]) and molecular assays (reverse transcription–polymerase chain reaction [RT-PCR]) have contributed to the ever-evolving nature of classification and diagnosis of soft tissue sarcomas. Over the past two decades, conventional karyotyping has demonstrated diagnostic utility in detecting a wide range of recurring numerical and structural chromosomal aberrations in soft tissue tumours.

Unlike the newer molecular techniques such as FISH, knowledge of the expected genetic change is not required and this enables karyotyping to function as a genome-wide screening tool. Furthermore, karyotyping can detect any further clonal progression in the event of a tumour relapse. The drawbacks of karyotyping include the dependency on sterile tumour specimens, success of growth culture, and being time-consuming.2

Histology, immunohistochemistry, and electron microscopy may sometimes show borderline or non-specific features. An example is that of malignant peripheral nerve sheath tumours which have been historically difficult to distinguish from other spindle cell sarcomas such as synovial sarcomas.3 Karyotyping has shown the main difference to be the presence of the (X;18) translocation.3 Many previous studies4 5 6 have also demonstrated the role of conventional karyotyping in the detection of clonal aberrations in 68% of malignant fibrous histiocytomas, and 38 to 48% of heterogeneous soft tissue sarcomas. Our study aimed to highlight the use of conventional karyotyping as a genome-wide screening tool, and also as an adjuvant diagnostic tool in the validation of histological diagnosis for soft tissue tumours.

Cytogenetic analysis involves a coordinated effort between surgical pathologists and cytogenetic laboratory technicians.6 In our study, fresh tumour samples were collected in sterile bottles from the surgical theatre and transported immediately to the cytogenetics laboratory. Next, the tumour specimens were washed 3 times with media containing Hank’s balanced salt solution, and 2% penicillin and streptomycin. After washing, the tissue was minced finely with scalpels and digested in collagenase II (GIBCO, Gaithersburg [MD], US) at a concentration of 1400 units/mL for 1 hour. The disaggregated tissue was then transferred into a centrifuge tube and washed twice with 1X Hank’s balanced salt solution and then with Roswell Park Memorial Institute complete medium (culture medium). The cells were centrifuged and transferred to a culture medium containing RPMI 1640, 20% fetal bovine serum, 2% 200 mmol/L L-glutamine, and 2% 5000 U penicillin and 5000 µg streptomycin.

Cells were cultured and harvested according to standard cytogenetic preparations and procedures. The cultures were set up in a 37°C incubator with 5% CO₂. The time of harvesting the cells depended on the degree of cell proliferation in culture. At harvest, 50 µL colcemid (10 µg/mL) was added to the cultures for 3 hours to arrest the cells at metaphase. Cultured cells were detached by treatment with 1X trypsin EDTA and then treated with 0.075 mol/L KCl-0.6% trisodium citrate solution (1:2) for 20 minutes at 37°C. After fixation in two changes of methanol-acetic acid (3:1), chromosome spreads were made by the air-drying method. Chromosomes were stained using the GTG banding method. A total of 20 cells were analysed in each case and karyotype results were designated according to International System of Human Cytogenetic Nomenclature (ISCN 2005, 2009).7 8

Conventional karyotyping of 35 consecutive fresh soft tissue tumour specimens was performed in a cytogenetic laboratory at our institution over a period of 4 years from 2005 to 2009. Medical records and histopathology reports for each patient case were reviewed and diagnoses were formulated based on the World Health Organization classification of soft tissue tumours.1 Recurrent chromosomal abnormalities were identified using the Mitelman Database of Chromosome Aberrations in Cancer,9 and with relevant literature search. Any novel chromosomal aberrations were also noted. This research protocol was approved by the ethics committee of our institution, and informed consent from the patients was obtained by the surgeon.

From January 2005 to March 2009, 35 consecutive fresh tissue specimens were harvested from soft tissue tumour surgical specimens. Histopathology results revealed 20 distinct morphologies. There were 29 malignant tumours, five benign tumours, and one of uncertain malignant potential. In our study, there was an almost equal gender representation with 18 males and 17 females, and age ranging from 15 to 81 years. Table 1 shows an overview of the patient’s age at diagnosis, tumour site, and tissue type for all 35 cases. The majority of our patients (37%) were in the age-group of 41 to 60 years. The most common tumour location was in the extremities (60%), and adipose tissue (34%) was the most common type. As shown in Table 2, conventional cytogenetic analysis revealed an abnormal karyotype detection rate of 63% (22 of 35 cases). Diagnostic abnormal karyotype was seen in nine (26%) cases—Ewing’s sarcomas (n=2), desmoplastic small round cell tumour (DSRCT) [n=1], synovial sarcomas (n=3), myxoid liposarcomas (MLPSs) [n=2], and lipoma (n=1). A normal karyotype (ie 46, XX or 46, XY) was seen in 11 (31%) cases. There were also two (6%) cases of culture failure. Table 3 shows the diagnosis, full karyotype results, and diagnostic utility for all 22 cases with abnormal karyotype.

A wide range of structural and numerical chromosomal abnormalities exists. These aberrations may be characterised by chromosomal gains or losses, balanced or unbalanced translocations, deletions or insertions, ring or marker chromosomes, or multiple complex karyotypes.6 Sarcomas may be categorised into two major cytogenetic groups: (i) sarcomas with tumour-specific chromosomal alterations and simple karyotypes2 10 11 or (ii) sarcomas with non-specific chromosomal alterations and complex unbalanced karyotypes.2 For group (i), karyotypes are considered to be tumour-specific or recurrent if the abnormality is found in two or more cases. For group (ii), a complex karyotype abnormality will not be specific for the diagnosis but is supportive of the diagnosis of malignancy. A ring chromosome may also indicate some form of malignancy. While a marker chromosome is diagnostically non-specific, it is an indicator of clonal progression and further testing by whole chromosome painting (CP) FISH may aid the diagnosis. Chromosome painting refers to the hybridisation of fluorescently labelled chromosome-specific probe pools for the detection of chromosomal aberrations.12 The simultaneous hybridisation of multiple CP probes, each tagged with a specific fluorochrome, enables the coloured display of all 24 human chromosomes also known as multicolour FISH.12 The advantages of CP include its ability to detect subtle telomeric translocations and small chromosomal markers, barely the size of a chromosomal band.12 Despite showing some utility as a genetic screening tool, CP is more straightforward only when used in conjunction with conventional cytogenetics which provide information on the specific chromosomes involved. This is because CP alone requires the iterative hybridisation of multiple CP probes, which is not always practical due to time constraints and limited specimens.12

Of the 22 cases with abnormal karyotype results, nine (41%) cases showed tumour-specific chromosome abnormalities. These nine cases had abnormal karyotypes which were consistent with the Mitelman Database of Chromosome Aberrations in Cancer9 and previously published literature.2 11 A normal karyotype was seen in 11 (31%) cases where three tumour tissues were of fibrous origin. One study in our literature search demonstrated a normal karyotype in 42% of cases; the majority of these were soft tissue tumours with a fibrous component or grossly dense matrix.6 The study rationalised that tumour cells embedded in a dense matrix were more difficult to culture.6 The two culture failure cases could have been due to specimen contamination or insufficient sample. A study conducted in a single institution in the United States (n=48) had documented an abnormal karyotype detection rate of 48% and a 10% culture failure rate in patients with soft tissue tumours.6 In contrast, our Asian cohort study had a higher detection rate of 63% (n=35) and a lower culture failure rate of 6%. The small sample size of this study was limited by the disease prevalence (rarity of sarcomas) as well as the logistics of obtaining fresh specimens from the surgical operating room. We intend to conduct future studies with a bigger sample size and explore other cytogenetic aberrations in soft tissue sarcomas using FISH in conjunction with conventional karyotyping.

Of the two cases of Ewing’s sarcoma in this study, one was a 42-year-old female (case 3; Table 3) and one a 26-year-old male (case 4; Table 3). This is an unusual clinical age-group for this sarcoma and the histological diagnosis was confirmed by karyotyping. In the male patient, the variant t(2;11;22)(q35;q24;q12) was demonstrated. For case 5 (Table 3), trisomy 12, a non-random secondary aberration, was demonstrated. One study found that the majority of chromosomal aberrations in Ewing’s sarcoma appear to be trisomy 8 and trisomy 12, occurring in 44% and 16% of Ewing’s sarcoma cases, respectively.13 14 15

Our study showed two diagnostic cases of synovial sarcoma (cases 19 and 20) with the hallmark translocation t(X;18) seen16 together with complex cytogenetic aberrations (Table 3). Another two cases of synovial sarcoma (cases 18 and 21) showed structure rearrangement on 2p/18p and translocation t(3;7)(q21;p13), respectively. These abnormalities were uncharacteristic. Histological biopsy of the left distal tibia showed a soft tissue tumour measuring 4 x 3 x 1 cm, composed of large sheets of malignant cells displaying high nuclear cytoplasmic ratio, round or irregular nuclei, nucleoli, scanty cytoplasm, and frequent mitoses. Tumour cells were positive for CD99 (MIC2 gene product), cytokeratin AE1+3 (especially epithelial-like areas), and vimentin. Further immunohistochemical staining with epithelial membrane antigen showed focal positivity. The soft tissue tumour had also invaded the distal tibia on the anteromedial and posteromedial aspects of the left leg with metastasis to the left groin lymph node. Case 21 was reviewed by various histopathologists and the general consensus was that of a high-grade undifferentiated synovial sarcoma. The representative karyogram for case 21 is shown in Figure 1.

In the study by Saboorian et al,17 there was one case of ambiguous histological results; the stained tissue smears showed densely cellular and tightly cohesive malignant spindle cells without discernible epithelial differentiation. A few differential diagnoses were formulated which included synovial sarcoma and karyotyping confirmed the diagnosis of synovial sarcoma by revealing the presence of t(X;18)(p11.2;q11.2).17 Another study by Akerman et al,18 which involved the cytogenetic evaluation of 15 surgical specimens, confirmed the (X;18) translocation as both a specific and sensitive marker for synovial sarcoma. Our study and the above studies serve to highlight the essential supportive role of conventional karyotyping in the confirmation of the diagnosis of synovial sarcoma.

Liposarcoma is the most common soft tissue sarcoma, accounting for 20% of mesenchymal neoplasms.19 It can be categorised into three subtypes: myxoid and round cell, well-differentiated, and pleomorphic.19 All three subtypes that were included in our study are discussed below.

Myxoid liposarcoma is the second most common liposarcoma subtype in which two thirds of the cases arise from the thigh musculature.19 The characteristic translocation t(12;16)(q13;p11) has been well documented in more than 90% of MLPS cases.19 20 21 22 This translocation leads to formation of a TLS-CHOP fusion gene (located at 12q13 and 16p11 respectively) which is highly sensitive and specific for MLPS.19 A possible trisomy 8 as an additional secondary change has also been reported.22 Our study demonstrated two cases of MLPS showing the t(12;16)(q13;p11) translocation. As shown in Table 3, this translocation was diagnostic of MLPS in cases 1 and 2. A study by the CHAMP group in which cytogenetic analysis was carried out in 28 MLPS specimens reported the t(12;16)(q13;p11) translocation in 26 cases; this further confirmed its consistency as a genetic marker for MLPS.20 Conventional karyotyping for t(12;16)(q13;p11) in MLPS was also shown to be useful as an adjunct diagnostic tool in poorly differentiated myxoid neoplasms in another study.21

Pleomorphic liposarcoma (PLPS) is the rarest (5% of liposarcoma) and most aggressive (highly metastatic) form of liposarcoma.19 It commonly affects the extremities in the elderly (>50 years) with an equal distribution in both genders.19 The complex structural abnormalities (unidentified marker chromosomes) and high chromosome counts (polyploidy) make it difficult to detect PLPS-specific aberrations.19 Our study demonstrated the case of a 77-year-old female (case 8; Table 3) with PLPS which showed complex, structural aberrations on karyotyping which, though not diagnostic, was indicative of a malignant clonal process.

Lipomas are the most common soft tissue tumours and are benign.23 One study by Sandberg and Bridge24 had documented rearrangements affecting the 12q13~q15 region as the most common aberration (65% of 188 lipomas). Clonal chromosomal aberrations were also reported in 60% of lipomas, and of these, 70% had normal cytogenetic cells.24 The most frequent t(3;12)(q27~q28;q13~q15) translocation was seen in 25% of lipoma cases.24

Case 10 (Table 3) belonging to a 53-year-old male demonstrated the balanced t(2;12) (q23;q15) translocation which was also novel in that the breakpoint 2q23 has not been previously reported. In this patient, histology showed a large lipoma measuring 14 x 9 x 8 cm. In addition, magnetic resonance imaging suggested a malignant liposarcoma. Szymanska et al25 found that the overrepresentation of 1q and 12q sequences was a recurrent finding in lipoma-like liposarcomas but not in lipomas. This is consistent with the chromosomal aberration involving 12q15 breakpoint in case 10. The representative karyogram for case 10 is shown in Figure 2.

Atypical lipomatous tumour (ALT) is synonymous with well-differentiated liposarcoma (WDLPS) as both exhibit similar cytogenetic findings regardless of location and pathology.19 Being the most common of all liposarcomas (40%-45%), ALT/WDLPS is an intermediate (locally aggressive) soft tissue sarcoma with mature adipocyte differentiation.1 19 26 Most ALTs are characterised cytogenetically by the presence of supernumerary ring chromosomes or long marker chromosomes involving chromosome region 12q13-15.26 27

Our study demonstrated abnormal karyotypes in two cases of ALT and WDLPS each. Of the two ALTs, case 6 (Table 3) had a ring chromosome as a sole abnormality and case 7 had supernumerary ring chromosomes present in addition to the multiple complex numerical structural aberrations. Case 11 (WDLPS) showed both complex numerical and structural chromosomal rearrangements in which two dicentric chromosomes were present together with ring chromosomes and giant marker chromosomes. Case 12 (WDLPS) belonged to a 65-year-old male; a normal karyotype was seen in 19 cells, one nonclonal abnormal cell was hypodiploid which showed trisomy 12, deletion on 12p, structural rearrangement on 20q as well as a ring chromosome. It is uncertain if this nonclonal abnormal cell is of any clinical significance. Histology had showed a WDLPS measuring 19 x 12 x 4 cm infiltrating the skeletal muscle of the left thigh.

It was reported that virtually all ALT/WDLPS had abnormal cytogenetic results.26 The CHAMP group conducted a study of 59 ALT/WDLPS and evaluated their relationship and differential diagnoses with other adipose tissue tumours.28 Clonal chromosomal abnormalities were found in 55 (93%) cases and supernumerary ring or giant marker chromosomes (RGCs) were seen in 37 (63%) cases28; RGCs were also shown to have tumour progression potential. Statistical analysis demonstrated a highly significant correlation between ALTs and RGCs (P<0.0001).28 The study reaffirmed the essential role of karyotype analysis in differentiating ALTs from benign lipomas, spindle/PLPS, hibernomas, and MLPS.

Desmoplastic small round cell tumour is a rare and aggressive neoplasm that commonly affects adolescents and young adults.29 30 Our study demonstrated the case of a 27-year-old male with DSRCT showing the classic t(11;22)(p13;q12) translocation (case 17; Table 3). In this case, histopathology reports showed no evidence of malignant infiltrates in the tumour specimen but conventional karyotyping confirmed the diagnosis to be DSRCT.

Karyotype analysis detected a majority (63%) of cases with abnormal chromosomes in our Asian cohort study with nine (41%) cases showing 22 abnormal karyotypes. Our study, hence, demonstrated that conventional karyotyping played an essential supportive role in validating histological diagnosis, especially in cases with borderline or complex morphology. Newer molecular techniques such as FISH and RT-PCR techniques may be sensitive but require prior knowledge of the expected genetic change. In view of this, conventional karyotyping is useful as a genome-wide screening tool in detecting single or multiple chromosomal aberrations in each patient. The use of conventional karyotyping is highly encouraged in the pursuit of discovering more novel recurring chromosomal aberrations.

This study was internally supported by the grant from the Department of Clinical Research and Cytogenetics Laboratory, Department of Pathology, Singapore General Hospital. The authors would like to thank Dr Alvin Lim for his support and Mr Lim Ping for his technical assistance in ensuring the success of this research project.

Obstructive sleep apnoea syndrome (OSAS) is characterised by repetitive, complete, or partial collapse of the pharyngeal airway during sleep and, generally, reduction in oxygen desaturation.1 The prevalence of OSAS is estimated to be 1% to 2% in men and 1.2% to 2.5% in women.2 The prevalence of OSAS in Turkey was reported as 1.8% in epidemiological studies.3

Sleep-disordered diseases are associated with a number of eye disorders including floppy eyelid syndrome, optic neuropathy, keratoconus, retinal vascular tortuosity and congestion, retinal bleeding, non-arteritic anterior ischaemic optic neuropathy and papilloedema secondary to increased intracranial pressure, normal tension glaucoma, and primary open-angle glaucoma (POAG).4 5 6 7 Sleep-disordered breathing may impair autoregulation of optic nerve perfusion due to the direct effect of hypoxia. Glaucoma is a multifactorial and specific optic neuropathy often characterised by increased intra-ocular pressure (IOP) that results in typical and progressive visual field loss.8

The prevalence of glaucoma in the general population is between 1% and 2%.9 While the aetiology of POAG still remains unclear, several risk factors have been associated with the condition. It was known that OSAS effects the oxygenation, neurohumoral factors, and vascular haemodynamics.4 It has been suggested that OSAS aggravates or even causes glaucoma by impaired optic nerve head blood flow and tissue atrophy, infarction due to vascular dysregulation or by direct damage to the optic nerve secondary to prolonged hypoxia.4 9

In addition to elevated IOP, cardiovascular risk factors—such as arterial hypotension and hypertension, vasospasms, autoregulatory defects, and atherosclerosis—are of increasing importance in the pathogenesis of glaucoma, especially in normal-tension glaucoma (NTG). Several recent reports4 5 10 11 suggest that OSAS may be an additional risk factor for glaucoma. Some of the possible causes of glaucoma-like abnormal blood coagulation, vasospastic disease, and optic nerve vascular dysregulation are also consequences of OSAS. It is not surprising, therefore, that some studies4 5 10 11 show an increased prevalence of OSAS in patients with glaucoma and vice versa. In clinical practice, OSAS is often not taken into diagnostic consideration in glaucoma patients.11

The association between glaucoma and OSAS has been reported in many studies. Most of them focused on the prevalence of glaucoma in OSAS patients and indicated it as a risk factor. Some of these articles have been observational case reports or case series.4 12 13 14 15 The objective of this study was to investigate the prevalence of OSAS in patients with POAG.

This was a prospective case series that included 30 consecutive adult POAG patients who attended the out-patient clinic of the Düzce University, School of Medicine, Turkey between July 2007 and February 2008. Informed consent was obtained from the study participants.

Individuals with diabetes mellitus (n=4), thyroid function disorders (n=2), hyperlipidaemia (n=2), and who refused to participate in the study (n=1) were excluded.

All patients underwent routine eye examination, including Snellen visual acuity, manifest refraction, slit-lamp examination of the anterior eye segment, IOP measurement, gonioscopy, and binocular examination of the optic disc.

Patients were considered to have POAG if they had untreated IOP of ≥21 mm Hg, an open anterior chamber angle, glaucomatous visual field defects or glaucomatous cupping of the optic disk, and no fundus or neurological lesion other than glaucomatous cupping to account for the visual field defect.

Prior to the sleep test, all POAG patients completed a questionnaire about sleep disturbance. Data from the questionnaire were used to evaluate basic OSAS symptoms such as snoring (presence of snoring for at least five nights per week), witnessed apnoea (spouse or relatives of patients with OSAS, identifying noisy and irregular snoring, and arrested respiration through the mouth and nose), and daytime sleepiness. The Epworth Sleepiness Scale was used to objectively evaluate excessive daytime sleepiness. If the score obtained on this scale was above 10, excessive daytime sleepiness was considered present.16 All POAG patients received an otorhinolaryngeal examination.

In addition, polysomnography (PSG; Somno-Medics Gmbh-8 Co. KG, Nonnengarten 8, D-97270 Kist Germany. Model: Somnoscreen-PSG, Ser-No: 0372 CAA5-OJ), electroencephalography, electro-oculography, chin electromyography, oral and nasal airflow (nasal-oral ‘thermistor’ and nasal cannula), thorax movements, abdominal movements, arterial oxygen saturation (pulse oximetry instrument), electrocardiogram, and snoring recordings (>6 hours) were obtained from all patients. All records were scored manually in a computer environment. Definitions of various terms are shown in the Box.17

Data were analysed using the Statistical Package for the Social Sciences (Windows version 10.0; SPSS Inc, Chicago [IL], US). Mann Whitney U test was used for comparing quantitative data. Chi squared test or Fisher’s exact test was used to compare categorical data. A P value of <0.05 was considered statistically significant. Spearman’s test was used for evaluating correlations between sample pairs.

Of the 21 POAG patients, 12 were female and 9 were male. Demographic and clinical features of the patients are summarised in Table 1.

Snoring was the most prevalent (81.0%) major symptom of OSAS; snoring was habitual in 42.9% of the patients. Daytime sleepiness and witnessed apnoea were found in 23.8% and 14.3% of the patients, respectively. While no major symptom was present in 52.4% of POAG patients, three major symptoms were concomitantly present in one (4.8%) POAG patient (Table 2).

Polysomnographic study showed that OSAS was present in 33.3% (n=7) of the POAG patients (apnoea-hypopnoea index [AHI] ≥5/hour). The severity of OSAS was mild (AHI of 5-15/hour) in 14.3% (n=3) and moderate (AHI of 16-30/hour) in 19.0% (n=4) of the patients. Age (P=0.047) and neck circumference (P=0.024) were significantly higher in POAG patients with OSAS versus those without OSAS; triceps skinfold thickness was also higher in OSAS patients, but it did not reach statistical significance (P=0.078). No significant difference was observed between POAG patients with and without OSAS with regard to body mass index and the duration of one or more major OSAS symptom (Table 3).

Primary open-angle glaucoma patients with and without OSAS did not differ significantly in terms of gender, smoking, hypertension, cup/disc ratio, and visual acuity. Intra-ocular pressure in POAG patients with OSAS was significantly lower than that in patients without OSAS (P=0.006 and P=0.035 for the right and left eyes, respectively). Apnoea-hypopnoea index was significantly higher (P<0.001) and the lowest desaturation on PSG was significantly lower (P=0.043) in POAG patients with OSAS than those without OSAS. Visual field defects were significantly more common in POAG patients with OSAS (P=0.038) [Table 4].

Obstructive sleep apnoea syndrome was not observed in POAG patients with no snoring (including simple snoring). As the degree of snoring increased, OSAS prevalence reached almost statistical significance. The symptoms of habitual snoring (P<0.001) and witnessed apnoea (P=0.026) were significantly more frequent in POAG patients with OSAS versus those without OSAS (Table 5).

No correlation was detected between PSG parameters (AHI, lowest desaturation in PSG) and ophthalmologic parameters (cup/disc ratio, visual acuity) in POAG patients (Table 6).

In this study, the prevalence of OSAS and the associated symptoms were higher in POAG patients than that in the general population.2 The prevalence of OSAS of at least mild severity was even higher compared with that in middle-aged adults (9% in women and 24% in men).3 Intra-ocular pressure levels in patients with OSAS were significantly lower than in those without OSAS. Another important finding of the present study was that there was a statistically significant but clinically insignificant difference between OSAS and non-OSAS patients regarding visual field defect.

Vascular risk factors for POAG have been hypothesised and researched. It has been reported that potential cardiovascular risk factors including systemic hypertension, atherosclerosis, vasospasm, and acute hypotension are associated with glaucoma.5 Nevertheless, some patients may experience progression of their neuropathy even though their IOP seems appropriately controlled. Obstructive sleep apnoea syndrome could be considered one of the risk factors for POAG. Since glaucomatous optic neuropathy is multifactorial, treatment of OSAS—which is currently a known and modifiable risk factor—may help the control of IOP and management of glaucoma.18

There are a few studies examining the correlation between POAG and OSAS. A recent study19 determined the prevalence of OSAS in POAG associated with snoring. Thirty-one snoring glaucomatous patients prospectively underwent PSG. Of these, 49% were diagnosed to have OSAS.19 Mojon et al4 performed overnight transcutaneous finger oximetry in 30 consecutive patients having POAG (mean age, 76.0 ± 7.9 years) and found that the oximetry disturbance index (ODI) was significantly higher (11%) in these patients compared with normal controls of the same age and sex distribution. They reported OSAS prevalence as 20% (n=6/30) in POAG patients according to ODI.4 In a group of 16 NTG patients, the OSAS prevalence was 50% in patients aged 45 to 64 years, and 63% in patients older than 64 years.10 We found an OSAS prevalence of 33.3% in POAG patients according to AHI.

Mojon et al5 reported a 7.2% prevalence of NTG among 69 white patients with OSAS (mean age, 52.6 ± 9.7 years), and it was significantly higher than that expected in general white population (2%).5 In another study, Sergi et al20 found a 59% prevalence of NTG in 51 OSAS patients (mean age, 64 ± 10 years). Contrary to the other studies, the prevalence of glaucoma in a study involving 228 patients with OSAS was reported to be the same as in the general population.21

Age is a common risk factor of both OSAS and POAG; the latter itself is an ageing-associated disease. The incidence of OSAS in the general population has been shown to be the highest between 45 and 65 years of age.22 Thus, high mean age (56.0 years) in our study might have contributed to the observed high prevalence of OSAS.

Snoring is known to be the most common symptom in OSAS.23 A group of out-patients, including those with POAG and without POAG, was recruited for evaluation of sleep-disordered breathing symptoms such as snoring, excessive daytime sleepiness, and insomnia with the help of a questionnaire.9 The authors reported high prevalence of sleep-disordered breathing in POAG patients. Compared with those without POAG, POAG patients showed a higher prevalence of snoring (47.6% vs 38.0%), snoring plus excessive daytime sleepiness (27.3% vs 17.3%), and snoring plus excessive daytime sleepiness plus insomnia (14.6% vs 7.8%).9 The authors speculated that the large nocturnal fluctuations in blood pressure of OSAS patients may have interfered with normal ocular haemodynamics, making the eye vulnerable to glaucoma.9 In the logistic regression model, snoring was significantly associated with glaucoma. However, that study was not a follow-up study of glaucomatous patients and snoring could not be accepted as a prognostic factor of POAG.9 Moreover, their study did not use objective measures such as overnight PSG for the diagnosis; instead, they only relied on self-reported symptoms.9 In another study,7 the prevalence of sleep-disordered breathing symptoms was higher in patients with NTG versus those without NTG (57% vs 3%). However, contrary to our study, they only offered PSG to patients with a positive sleep history.7 In our study, the prevalence rates of snoring, habitual snoring, witnessed apnoea, excessive daytime sleepiness were 81.0%, 42.9%, 14.3%, and 23.8%, respectively. The concomitant presence of two or three major OSAS symptoms was observed in 23.8% and 4.8% of our POAG patients, respectively. Blumen Ohana et al19 reported high prevalence of OSAS in patients with POAG and suggested that presence of snoring should be explored at interview. Conversely, patients who snore should be asked whether they have POAG, and if so, should undergo all-night sleep recording for the presence of OSAS.19 Mojon et al5 also found that respiratory disturbance index (RDI) was positively correlated with IOP in 114 OSAS patients. Because of the observational nature of that study, they concluded only an association between glaucoma and OSAS rather than a direct causal relationship.5 A study by Karakucuk et al15 found that the prevalence of glaucoma in patients with OSAS was 12.9% (n=4/31); all these four patients with glaucoma were in the severe OSAS group. There was also a positive correlation between IOP and AHI, and they suggested that increased IOP values may reflect the severity of OSAS.15 In another cross-sectional study, there was no correlation between IOP and RDI.21 In the present study, IOP level in patients with OSAS was significantly lower than that in those without OSAS. Intra-ocular pressure shows diurnal variation and patients with OSAS may have elevated IOP and perfusional disturbance of retinal nerve fibres during sleep. Therefore, these patients may have completely normal or low IOP during the daytime. On the other hand, most patients with OSAS were regularly under glaucoma medication which lowers the IOP to within normal limits.

Sergi et al20 did not find any difference in the cup/disk ratio between the study patients and the control group. They found a significant correlation between AHI and the cup/disk ratio but none between awake arterial blood gases and the ophthalmologic examination data.20 They speculate that POAG could be a consequence of changes in vascular tone and of the increased platelet aggregability which frequently occur in OSAS patients. In contrast with their study, our study shows that the cup/disk ratio did not differ between POAG patients with and without OSAS.

A study in Hong Kong24 examined the computerised visual fields and optic discs of OSAS patients with normal IOP and compared these with non-OSAS population. Visual field indices were significantly lower and the incidence of suspicious glaucomatous disc changes was higher versus the control arm.24 A variety of visual field defects in OSAS patients were also reported by Mojon et al25 in nine patients; the field defects stabilised in two of these after 18 months following continuous positive airway pressure (CPAP). Kremmer et al11 have also reported patients with NTG and progressive field loss despite IOP-lowering eye drops and surgery. Nevertheless, they stabilised field loss of patients after diagnosis of OSAS and treatment with CPAP.11 Although there was statistically significant difference in the visual field defects of POAG patients with and without OSAS in our study, it was clinically insignificant. Only significant glaucomatous visual field defects were considered in our evaluation. Therefore, minor changes due to lenticular opacifications or other aetiology were not taken into account as major glaucomatous visual field changes.

Hypoxaemia and haemodynamic changes resulting from intermittent apnoea and hypopnoea during sleep are believed to play a role in glaucomatous optic neuropathy.21 Although there is no clear evidence for a cause-effect relationship in the present study, the high prevalence of OSAS in patients with POAG suggests a possible relationship.

In this study, the prevalence of OSAS was higher in POAG patients versus the general population. In clinical practice, OSAS is often not taken into diagnostic consideration in glaucoma patients. The high prevalence of OSAS in patients with POAG suggests the need to explore the long-term results of coincidence, relationship, and cross-interaction between these two common disorders. Based on data from the present study, we recommend that the history of sleep apnoea symptoms be asked in patients with glaucoma, especially in those who are obese and have thick necks. In addition, PSG should be performed in those patients with two or more major sleep disturbance symptoms. Further large-scale studies are required to explore the long-term results of these two common disorders, particularly in patients who have been treated with CPAP therapy.

Rectal cancer is associated with a high risk of distant metastases as well as local recurrence. The reported local recurrence rate after surgical treatment was up to 32% in some older literatures.1 Recently, magnetic resonance imaging (MRI) has emerged as a powerful local staging tool which also helps to guide subsequent management plan.2 3 The status of circumferential resection margin (CRM), presence of lymph node metastasis, and location of the tumour, all of which can be predicted on MRI, are important prognostic factors for pelvic disease recurrence after treatment with curative intent (local failure).4 5 6

The depth of extramural penetration of the tumour has been shown to be an independent prognostic factor.7 According to the European Society for Medical Oncology guidelines,8 T3 disease is subclassified into T3a, T3b, T3c, and T3d based on the depth of invasion beyond the muscularis propria (Table 1). Magnetic resonance imaging is also highly accurate in predicting the actual depth of this invasion.9 Currently, patients with disease more advanced than T3b are recommended to receive induction therapy prior to surgery.

Another factor that potentially affects the disease status is the thickness of the mesorectal fat which, for the sake of this discussion, shall be defined as the distance between the serosa and mesorectal fascia. The word ‘perirectal fat’ is used interchangeably with ‘mesorectal fat’. We are of the opinion that the word ‘mesorectal fat’ better conceptualises compartmentalised fat within the mesorectal fascia and is, thus, selected for use in this article.

In our experience, the mesorectal fat is rather thin in Chinese patients. It is not uncommon to encounter early T3 (T3a/b) disease with threatened CRM as predicted on MRI. The less the mesorectal fat thickness, the less the depth of extramural invasion it takes to infiltrate the CRM.

This study aimed to measure the amount of mesorectal fat in the local population. The use and limitation of T3 subclassification in the Chinese population will be discussed.

A total of 25 consecutive staging MRIs done for patients referred for rectal carcinoma multidisciplinary meetings at a local regional hospital from January to October 2012 were retrospectively reviewed by two radiologists with special interest in abdominal imaging.

All MRI examinations were acquired with 1.5T MRIs in two local centres using Siemens Magnetom Avanto (Erlangen, Germany) MRI machines. Measurements were made with mutual agreement between the two reviewing radiologists. The thickness of mesorectal fat was defined as the distance from the serosa to the mesorectal fascia in the axial plane. The distance in mm was obtained in the true axial plane at levels of 5 cm, 7.5 cm, and 10 cm from the anal verge. Measurements were performed primarily on T2 sequence, supplemented by T1 sequence if the acquired T2 images were unsatisfactory. As this study involved two hospitals, the scanning parameter was not identical. However, such difference was not assumed to attribute to error of any source in terms of calibre measurement.

Four readings were obtained at each level, namely, anterior, left lateral, posterior, and right lateral positions (Fig 1).

Patients with bulky primary or secondary pelvic tumours (>3 cm in diameter) were excluded from the study, as these might potentially cause significant distortion of the anatomy and configuration of the mesorectum.

Statistical analysis was performed with the Statistical Package for the Social Sciences (Windows version 15.0; SPSS Inc, Chicago [IL], US). One-sample Student’s t test was performed for analysis of mean thickness.

A total of 25 patients (16 males, 9 females) with a median age of 69 (range, 38-84) years were included in the study. The rectosigmoid junctions were reached at the level of 10 cm above the anal verge for four patients and were, thus, excluded from calculation for the respective level.

Mean thicknesses of mesorectal fat at 5 cm, 7.5 cm, and 10 cm from the anal verge were 3.1 (standard deviation [SD]=3.0) mm, 9.8 (SD=5.3) mm, and 11.8 (SD=4.2) mm, respectively. Details of the mean mesorectal fat thickness are shown in Table 2. In brief, the proportions of patients with mean mesorectal fat thickness of <15 mm were 100%, 84%, and 75% at 5 cm, 7.5 cm, and 10 cm from the anal verge, respectively.

The mesorectal fat was noted to be the least thick in the anterior position for all three arbitrary levels (Table 2; Fig 2). At 5 cm and 7.5 cm from the anal verge, proportions of patients with mesorectal fat thickness of <5 mm were 96% and 88%, respectively. The figure reached up to 100% if 15 mm was taken as the cutoff level. At 10 cm from the anal verge, 95% of patients showed mesorectal fat thickness of <15 mm. t Tests showed that the anterior mesorectal fat thickness was significantly <15 mm at all three levels (P<0.001) and <5 mm at both 5 cm (P<0.001) and 7.5 cm (P=0.01) from the anal verge (Table 3).

There was a tendency for the lateral aspects to be more spacious than the anterior and posterior aspects, and for the left side to be larger than the right side. However, these findings were not statistically significant.

To the best of our knowledge, this is the first Chinese study and the first study in Asian subjects on mesorectal fat thickness. The majority of published literature on MRI staging of carcinoma of rectum are based, predominantly, on data from western/Caucasian populations. It has been well known that variations in body build, lean mass, and fat composition do occur across ethnic groups.10 Chinese or Asian patients have a smaller body build. Whether the amount of fat in the mesorectum is the same in Chinese and Caucasian population remains largely unknown.

In recent decades, total mesorectal excision has revolutionised rectal cancer surgery.11 Patients with relatively early tumours (ie T3b or below, lymph node–negative) are usually streamlined to total mesorectal excision without preoperative neoadjuvant therapy. The rationale behind this is that early, mid- and low-rectal tumours with their whole lymphatic drainage are contained within the mesorectal fascia. Total mesorectal excision allows en-bloc removal of the tumour together with its intact mesorectal fascia. A low local recurrence rate of only 4% has been reported.12

An involved CRM is an independent disease prognostic indicator.13 It is defined pathologically as identifying tumour cells within 1 mm of the surgically created margin. Beets-Tan et al14 postulated that, on MRI, a distance of 6 mm from the outer edge of the tumour to the mesorectal fascia predicted a tumour distance of 2 mm on histology with 97% confidence, and a distance of 5 mm could predict a crucial distance of 1 mm on histology with high confidence. A study using 1 mm as cutoff showed data with satisfactory accuracy despite a lower sensitivity.15 For practical purposes, we have adopted a cutoff of 5 mm as the predictor of clear CRM.

Given a certain depth of tumour invasion, CRM is more likely to be threatened for patients with thinner mesorectal fat (Fig 3). The mean thickness of mesorectal fat is <15 mm for the majority of patients at all arbitrarily measured levels. Taking into account the margin of 5 mm on MRI, a tumour invading 10 mm beyond the serosa on MRI fulfils the criteria for threatened CRM in the majority of patients. Whether Chinese patients present with later-stage disease or have worse disease prognosis is largely unknown. However, caution has to be taken that T3a/b disease in Chinese populations does not equal, or even imply, early-stage disease.

The position of the tumour may also affect the chance of mesorectal fat infiltration. The anterior aspect of the mesorectal fat was found to be thinnest at all three arbitrary levels. This is in agreement with studies in European populations.16 The postulated reason is that the anterior mesorectal fat tends to be compressed by anterior pelvic organs such as the uterus and prostate when one lies in supine position, the position where MRI is conventionally acquired. As a result, anterior tumour tends to threaten the CRM with relatively shallow subserosal penetration.

The mesorectal fat is thinner inferiorly as it approaches the anal verge. Low rectal cancer (<5 cm from the anal verge) has overall worse prognosis. Higher local recurrence rate with higher chances of CRM involvement has been reported.17 This may be partly explained by the fact that the amount of mesorectal fat is thinner in low rectum. Low rectal tumours also deserve special surgical attention.18

One major weakness of this study was that body mass index (BMI) was not taken into account. However, a study in the UK19 has shown that BMI does not affect the thickness or volume of mesorectal fat. However, the measurement method employed in that study was different from that in our study, rendering direct comparison difficult. Whether the paucity of mesorectal fat in Chinese patients is due to body build or genetic factors is unknown. Further multicentre studies with collection of BMI data and ethnic information and using standardised measurement methods are needed for better comparison.

Thickness of mesorectal fat is shown to be <15 mm in the majority of patients in most positions and at most levels. It was <5 mm for low rectal position. T3a/b tumours may paradoxically infiltrate the mesorectal fascia in the study population. In staging of Chinese rectal cancer patients, T3a/b tumours may threaten the CRM in the majority of locations and patients. Thus, the status of T3a/b alone should not be taken as an indicator of early-stage disease.

We would like to acknowledge Dr John KW Chan and St Paul’s Hospital for courtesy of MRI images.