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Review of sleep studies of patients with chronic insomnia at a sleep disorder unit.

INTRODUCTION
Chronic insomnia is associated with many physical and psychiatric illnesses, and its underlying aetiology needs to be identified in order to achieve safe and effective treatment. Obstructive sleep apnoea (OSA) and periodic limb movement disorder (PLMD) are common primary sleep disorders that can lead to chronic insomnia. Patients with these conditions are evaluated using polysomnography (PSG).


METHODS
The PSG records of 106 patients with chronic insomnia who presented to a multidisciplinary sleep clinic in Singapore over a five-year period were reviewed. To examine the utility of PSG in the evaluation of chronic insomnia, the clinical diagnoses of the patients before and after the sleep studies were compared.


RESULTS
Among the 106 patients, 69 (65.4%) were suspected to have primary sleep disorders based on clinical history and examination alone. Following PSG evaluation, 42.5% and 4.7% of the study population were diagnosed with OSA and PLMD, respectively. OSA was found in 35.9% of the 39 patients who had underlying psychiatric conditions.


CONCLUSION
This study illustrates that many patients with chronic insomnia have underlying primary sleep disorders. It also highlights the danger of attributing chronic insomnia in psychiatric patients to their illness, without giving due consideration to other possible aetiologies. Clinicians should maintain a high index of suspicion for the presence of other aetiologies, and make timely and targeted referrals for sleep studies where appropriate.