A comparison of multiple and single sleep latency and cerebral evoked potential (P300) measures in the assessment of excessive daytime sleepiness in narcolepsy-cataplexy.

A direct comparison was made between the amplitude of evoked potential (EP) component P3 (by the P300 paradigm), a known sensitive EP correlate of sleepiness, and sleep latency measures (both to stage 1 or rapid eye movement [REM] and to stage 2 or REM) of the Multiple Sleep Latency Test (MSLT) in 11 untreated narcoleptics and matched controls. Repeated P3 measures were performed immediately prior to standard MSLT naps at 10:00 a.m., 12:00 noon, 2:00 p.m., 4:00 p.m., and 6:00 p.m. Using discriminant analysis and F tests, all three measures (P3 and both by MSLT) were found to distinguish the two groups for collapsed five-nap data, and all showed essentially parallel circadian time-of-day effects, with greatest sleepiness in the midafternoon. The MSLT, however, was somewhat more powerful for collapsed data. Both tests misclassified some subjects as belonging to the other group, with greater misclassification for both tests in the control group and more overall for the P3 measure. Adding the two sleep onset REM period (SOREMP) criteria on MSLT for narcolepsy, one patient was still classified as normal. Analysis of data from individual naps indicated that the MSLT was considerably more powerful in discriminating groups than was P3 amplitude, and it did so for all five naps.