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The studies examined in this review indicate that the MSL is sensitive to conditions expected to increase sleepiness. MSL are generally lower following sleep loss, following use of sedating medications, during wakefulness in the late night or early morning hours, and among patients with sleep disorders associated with excessive sleepiness such as narcolepsy or obstructive sleep apnea. However, the wide range in MSL makes it difficult to establish a specific threshold value for excessive sleepiness or to discriminate patients with sleep disorders from non-patients. Some of this variation may be attributable to methodological differences and some may be attributable to individual differences in sleep tendency (e.g., related to age). The studies analyzed in this review indicate that the MSL on both the MSLT and MWT does not discriminate well between patients with sleep disorders and normal populations. This is due to large SD as well as floor or ceiling effects in the tests. However, the MSL shows appropriate change from initial testing to subsequent testing following treatment or manipulations intended to alter sleepiness or alertness. Additionally the presence of two or more SOREMPs on the MSLT is a common finding in narcolepsy patients. However, SOREMPs are not exclusive to narcolepsy patients but are frequent in untreated sleep apnea

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SummaryExcessive daytime sleepiness is a complaint characterizing many disorders of the wakefulnesssleep cycle. This paper addresses the complaint of sleepiness objectively by an attempt to differentiate a group of control subjects from a group of patients with unambiguous narcolepsy. Fourteen control and 27 narcoleptic subjects were evaluated by one of three protocols involving nocturnal recordings, detailed interviews, and 5 or more 20-min opportunities to sleep offered at 2-h intervals beginning at 10.00 o'clock, ±30 min. Each 20-min opportunity to sleep was given to subjects lying in a darkened quiet room and asked to try to fall asleep. Polysomnographic variables were monitored and sleep was scored in 30-sec epochs by standard criteria. The interval from the start of each test to the first epoch of NREM (including stage 1 sleep) or REM sleep was called sleep latency. In two of the protocols, the subjects were awakened immediately after sleep onset. In the third protocol, the subjects were awakened after 10 min of sleep. Narcoleptics consistently fell asleep much more readily than did control subjects. We conclude that the Multiple Sleep Latency test, in addition to providing opportunities to clinically document sleep onset REM sleep periods, can demonstrate pathological sleepiness. Based on these data, we suggest that an average sleep latency less than 5 min be set as the minimum cutoff point for pathological sleepiness.Excessive daytime sleepiness (EDS) is a complaint characterizing many disorders of the wakefulness-sleep cycle (Guilleminault and Dement 1977). Despite the potential dangers to life and property of EDS, complaints are frequently unevaluated by physicians because there are few objective tools available to confirm pathological sleepiness.Traditional approaches to the study of sleepiness have included performance tests such as those developed to evaluate the consequences of sleep deprivation and various work-rest schedules (e.g., Wilkinson el al. 1968), and pupillography (Yoss et al. 1969). These approaches rely on a statistical relationship between an operational definition of sleep deprivation or a subjective measurement of sleepiness on the one hand and a behavioral or psychophysiological parameter on the other hand.More recently, Carskadon and Dement (1977) suggested that sleep latency (defined as the time between the point when an individual tries to sleep and the point when electroencephalographic patterns of sleep first develop) measured repeatedly in controlled nap situations might prove a useful tool in evaluating pathological sleepiness.Such a multiple nap procedure offers several advantages over performance testing, subjective tests, and pupillography. First, the concept of sleep latency as a measure of sleepiness has face validity, since presumably one who is sleepy will fall asleep more quickly than one who is not sleepy. Second, the use of sleep latency as a measurement of sleepiness is less subject to the confounding influences of muscle fatigue, motivation and practice than are...