Determination of Sleep Latency in Polysomnographic Evaluations of Daytime Somnolence in Patients with Sleep Apnea and Patients with Narcolepsy

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Abstract
Sleep onset during the multiple sleep latency test was scored by three criteria for 21 patients with narcolepsy and 21 patients with obstructive sleep apnea: a single epoch of stage 1, three consecutive epochs of stage 1, and a single epoch of stage 2 or REM. Mean sleep latency for both groups was predictably shortest using a single epoch of stage 1 and longest using a single epoch of stage 2 or REM. All estimates of sleep latency were highly correlated. It was concluded that a single epoch of any stage of sleep is an appropriate measure of sleep latency for patients with narcolepsy, although a modified scoring system should be developed for patients with sleep apnea. The obstructive apneic episodes prevented or delayed sleep onset on 4.8% to 33.3% of trials depending on the specific criteria used to determine sleep latency. Such apnea-related interruptions to sleep should be taken into account when assessing daytime somnolence in patients with sleep apnea.