Sleep latency on the maintenance of wakefulness test (MWT) for 530 patients with narcolepsy while free of psychoactive drugs

Abstract

Objectives: To compare maintenance of wakefulness test (MWT) data gathered at baseline in the course of two, multicenter studies on the therapeutic efficacy of modafinil with published MWT norms.

Methods: The MWT is a procedure that uses electrophysiological measures to determine the ability to remain awake while sitting in a quiet, darkened room. The test consists of 4 20 min trials conducted 4 times at 2 h intervals commencing 2 h after awakening from a night of sleep. MWT data were gathered at baseline in the course of two, multicenter studies on the therapeutic efficacy of modafinil. Subjects were 17-68 year old men (n = 239) and women (n = 291) diagnosed with narcolepsy according to the International Classification of Sleep Disorders (ICSD). All patients were free of psychoactive medication for a minimum of 14 days.

Results: Mean MWT sleep latency was 6.0 +/- 4.8 min. However, the mean for the first MWT trial was 7.0 min which was longer that the means for the following 3 trials (5.8, 5.6 and 5.7 min, respectively). The 4 distributions of the individual MWT trials were similar and adequately summarized by the distribution of the average MWT sleep latency. As a group, patients with narcolepsy were less able to remain awake than normals; only 8 of 530 (1.5%) patients were able to remain awake on 4 20 min MWT trials compared with 35 of 64 (54.7%) normals in another study. However, using a mean MWT sleep latency of 12 min (the 5th percentile for normals) as the lowest cut-point for normalcy, 15% of patients with narcolepsy appeared to have an unimpaired ability to remain awake.

Conclusions: The diagnosis of narcolepsy did not always predict inability to remain awake on the MWT. Age, gender and the duration of illness did not predict ability to remain awake. Patients with severe cataplexy and other ancillary symptoms were least able to remain awake on MWT trials. Patients who used tobacco and caffeine moderately had the lowest MWT sleep latencies relative to patients with heavy and light use.