VALUE OF THE MULTIPLE SLEEP LATENCY TEST (MSLT) FOR THE DIAGNOSIS OF NARCOLEPSY

Since its introduction, the multiple sleep latency test (MSLT) has pla yed a major role in the diagnosis of narcolepsy. We assessed its diagn ostic value in a series of 2,083 subjects of whom 170 (8.2%) were diag nosed with narcolepsy. The sensitivity of the combination of two or mo re sleep onset rapid eye movement (REM) periods (SOREMPs) with a mean sleep latency of <5 minutes on an initial MSLT was 70% with a specific ity of 97%, but 30% of all subjects with this combination of findings did not have narcolepsy. In some narcoleptics who had more than one MS LT, the proportion of naps with SOREMPs varied substantially from the initial MSLT to the follow-up test. The highest specificity (99.2%) an d positive predictive value (PPV) (87%) for MSLT findings was obtained with the criteria of three or more SOREMPs combined with a mean sleep latency of <5 minutes, but the sensitivity of this combination was on ly 46%. The combination of a SOREMP with a sleep latency <10 minutes o n polysomnography yielded a specificity (98.9%) and PPV (73%) almost e qual to those obtained from combinations of MSLT findings, but the sen sitivity was much lower. Our results suggest that the MSLT cannot be u sed in isolation to confirm or exclude narcolepsy, is indicated only i n selected patients with excessive daytime sleepiness, and is most val uable when interpreted in conjunction with clinical findings.