The usefulness of five nap opportunities in multiple sleep latency tests for the diagnosis of narcolepsy

Background: Narcolepsy is a rare, chronic disorder that affects the regulation of the sleep wake cycle. The main manifestations are excessive daytime sleepiness, cataplexy, sleep fragmentation, hypnagogic hallucinations and sleep paralysis. The Multiple Sleep Latency Test (MSLT) is a valuable diagnostic tool for narcolepsy. During the test individuals are given 4 or 5 nap opportunities and the tendency to fall asleep is measured. Aim of the study: This is the first study that aimed to look specifically at the usefulness of a 5th nap opportunity in the MSLT. Methods: Data was retrospectively collected from the Sleep Disorders Centre of a Tertiary Hospital on patients that had a 5th nap during their MSLT over a 3-year period. A full medical history was available for each patient and each subject who would have also undergone a full night polysomnography the night before the MSLT. Results: A total of 53 patients had a 5th nap performed out of 378 MSLT studies. In 16% of cases a diagnosis of narcolepsy was given directly due to the inclusion of the 5th nap on the MSLT. Here a 5th nap allowed diagnostic criteria of mean sleep latency 2 SOREMPS (Sleep Onset REM Periods) to be met. In 53% of cases the mean sleep latency increased due to 5th nap inclusion; the mean sleep latency of the first four naps was 5.6 vs. 6.7 after inclusion of the 5th nap. Conclusion: Our study shows that only a few patients may benefit from a 5 naps MSLT, although this extra nap may be important for the establishment of a diagnosis given a history suggestive of narcolepsy. On a routine basis the extra nap might not be helpful as it may increase time, cost and patient anxiety.