CORRELATES OF SLEEP LATENCY ON THE MULTIPLE SLEEP LATENCY TEST IN A CLINICAL POPULATION

The multiple sleep latency test (MSLT) is commonly used as an objectiv e measure of sleepiness. We retrospectively correlated MSLT scores fro m 147 patients with other information relating to sleepiness, namely d emographic information, data from nocturnal polysomnograms (PSGs), and subjective assessments. The only variable that showed a valid and sta tistically significant correlation with the MSLT score was sleep laten cy on the PSG. The results were largely similar within subgroups focus ing on (1) individuals with the ability to fall asleep on every nap, ( 2) subjects with abnormally short MSLT scores, (3) nap attempts that w ere successful, and (4) patients with particular diagnoses. We conclud e that the mean sleep latency on the MSLT, in a clinical population, d oes not correlate well with a number of variables expected to influenc e sleepiness. While the validated utility of the MSLT in separating pa tients from normals or in identifying narcolepsy is not disputed, the accuracy of the MSLT as a measure of sleepiness appears to be limited.