The Value of Repeated Non-confirmatory Multiple Sleep Latency Test (MSLT) for the Diagnosis of Narcolepsy

Aim: Narcolepsy is confirmed if the MSLT (Multiple Sleep Latency Test) shows the mean sleep latency of <= 8 min and >= 2 episodes of sleep with early onset of REM sleep. The aim was to assess the value of repeated MSLT in subjects with suspected narcolepsy after the first MSLT failed to confirm narcolepsy. Patients and methods: This is a retrospective study of the MSLT results in adult patients examined for narcolepsy at the Sleep and Wake Disorders Center of the Department of Neurology, First Faculty of Medicine and General University Hospital in Prague during a 13-year period. The study analysed 39 adults with suspected narcolepsy who underwent second MSLT in a course of one year after their first MSLT results failed to meet the criteria for narcolepsy, and 42 patients whose initial MSLT was consistent with narcolepsy. Results: In 19 patients, the first MSLT was negative, while the second was positive. In 20 patients, both the first and repeated MSLT failed to meet the diagnostic criteria for narcolepsy. These groups differed from one another and from patients diagnosed with the first MSLT in REM sleep latency during nocturnal polysomnography. Sleep latency in the first test is predictive of the outcome of the repeated MSLT (p < 0.001). Sensitivity of one MSLT compared to two is 82.4%, and negative predictive value of the first non-confirmatory test is 48%. Conclusions: It is useful to repeat testing in patients with suspected narcolepsy and inconclusive MSLT.