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OSA in Antipsychotic Users — MRCPsych Paper B MCQ

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HardSchizophrenia & PsychosisOSA in Antipsychotic UsersMRCPsych Paper B

A 40-year-old man with schizophrenia has taken olanzapine 20 mg at night at an unchanged dose for 18 months. Over the past 6 months he has developed marked daytime somnolence, morning headaches and nocturia. His BMI is 42 kg/m², neck circumference is 48 cm and blood pressure is 148/92 mmHg. His partner describes loud snoring with recurrent pauses in breathing followed by gasping. He reports no cataplexy, sleep paralysis or irresistible urge to move his legs. His awake arterialised capillary PaCO2 is 5.3 kPa. Which comorbid sleep disorder should be prioritised for objective investigation before attributing his somnolence to olanzapine?

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Correct answer: E — Obstructive sleep apnoea/hypopnoea syndrome

The correct answer is E, obstructive sleep apnoea/hypopnoea syndrome. Loud snoring, witnessed breathing pauses with gasping and excessive daytime somnolence form the characteristic syndrome, with severe obesity, large neck circumference and hypertension increasing the likelihood. NICE recommends assessment when at least two suggestive features are present and recommends home respiratory polygraphy as the initial diagnostic test. Olanzapine can cause sedation and weight gain, but the nocturnal respiratory features should not be explained by medication alone. Narcolepsy type 1 would require features such as cataplexy or REM-sleep intrusion. Idiopathic hypersomnia does not explain witnessed apnoeas. Obesity hypoventilation syndrome requires raised awake PaCO2, which is absent. Restless legs syndrome causes an urge to move the legs rather than obstructive breathing events.

Reference: National Institute for Health and Care Excellence. NG202: Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s, sections 1.1 and 1.3, 2021 (links updated 2025). https://www.nice.org.uk/guidance/NG202/chapter/1-obstructive-sleep-apnoeahypopnoea-syndrome