The prevalence of syndrome Z (the interaction of obstructive sleep apnoea with the metabolic syndrome) in a teaching hospital in Singapore

Background: Syndrome Z describes the interaction of obstructive sleep apnoea (OSA) with the metabolic syndrome. Purpose of study: A pilot study to determine the prevalence of syndrome Z in a teaching hospital in Singapore. Methods: Patients ( age > 18 years) recruited for this prospective study had to satisfy three of the following five inclusion criteria: fasting glucose > 6.1 mmol/ l, blood pressure >= 130/ 85 mm Hg, HDL cholesterol,1.04 mmol/ l in men and,1.2 mmol/ l in women, triglycerides > 1.7 mmol/ l, and a waist circumference > 102 cm in men and > 88 cm in women. All subjects underwent standard overnight polysomnography. Overnight fasting glucose and lipid levels were measured and baseline anthropometric data recorded. All sleep studies were scored and reported by a sleep physician. OSA was deemed to be present if the respiratory disturbance index (RDI) was >= 5, with mild, moderate and severe categories classified according to the Chicago criteria. Results: There were 24 patients ( 19 males and five females) of whom 10 were Chinese, eight Malay and five of Indian origin, with one other. Mean age was 48 +/- 13.5 years, mean body mass index was 34.9 +/- 6.1 kg/ m(2) and mean waist circumference was 111.3 +/- 15.7 cm. 23 (95.8%) of the patients had OSA with a mean RDI of 39.6 +/- 22.4 events/h with 15 patients (62.5%) in the severe category. The five patients who fulfilled all five criteria for diagnosis of the metabolic syndrome had severe OSA. Conclusion: The prevalence of OSA in our studied population exhibiting the metabolic syndrome is very high. Therefore, a polysomnogram should always be considered for this subset of patients.