MSLT in primary insomnia: stability and relation to nocturnal sleep

To assess the stability of the multiple sleep latency test (MSLT) in primary insomnia and its relation to total sleep time.

Randomized, double-blind, placebo controlled, clinical trial.

Outpatient with sleep laboratory assessments in months 1 and 8 of treatment.

Ninety-five primary insomniacs, 32-64 years old and 55 age- and sex-matched general population-based, representative controls.

After a screening nocturnal polysomnograms (NPSG) and MSLT the following day, participants with primary insomnia were randomized to take zolpidem 10 mg (n = 50) or placebo (n = 45) nightly for 12 months. During months 1 and 8, while taking their prescribed treatments, NPSGs and MSLTs the following day were conducted. A population-based sample served as controls and received a single NPSG followed by MSLT.

Mean daily sleep latency on the screening MSLT of insomniacs was normally distributed across the full range of MSLT scores and significantly higher than those of a population-based representative control sample (P < 0.006). The insomniacs with the highest screening MSLTs had the shortest screening total sleep times (P < 0.05). The MSLTs of insomniacs during treatment in study month 1 were correlated (r = 0.44, P < 0.001) with their month 8 MSLT. The mean MSLT score of the zolpidem group did not differ from that of the placebo group, and the stability within treatment groups also did not differ.

These data support the hypothesis that some insomniacs show a reliable disorder of hyperarousal with increased wake drive both at night and during the day.