The Usefulness of Repeated Multiple Sleep Latency Test for the Diagnosis of Narcolepsy

Abstract

Background: Multiple Sleep Latency Test (MSLT) has been used as an objective measure of daytime sleepiness and for the diagnosis of narcolepsy. However, the MSLT’s current criteria for narcolepsy may miss narcolepsy. To investigate the usefulness of repeated MSLT for increasing the sensitivity of narcolepsy diagnosis, we performed the second MSLT in patients whose clinical history includes excessive daytime sleepiness with or without cataplexy but the first MSLT result did not meet the criteria for narcolepsy. Method: MSLT was repeated in 27 patients with excessive daytime sleepiness. Each patient had an overnight polysomnography and the first MSLT in next day. The 2nd MSLT was performed 1-3 months after the first MSLT. Five nap trials were done in each MSLT. Result: In the 2nd MSLT, nine of 27 patients (33%) with an initial MSLT that did not satisfy the diagnostic criteria of narcolepsy, met the MSLT criteria for narcolepsy (Mean sleep latency < 8 min and two or more sleep-onset REM periods). The other 16 patients were diagnosed as idiopathic hypersomnia. Four patients whose history has excessive daytime sleepiness with cataplexy didn’t meet the MSLT criteria for narcolepsy in both first and second MSLTs. Conclusion: Our findings suggest that repeated MSLT is valuable for the diagnosis of narcolepsy in patients with suspected narcolepsy but insufficient result of the first MSLT for narcolepsy criteria.