Non-random temporal distribution of sleep onset REM periods in the MSLT in narcolepsy

Abstract

The diagnosis of narcolepsy is supported by the presence of two or more sleep onset REM periods (SOREMPs) in the multiple latency sleep test (MSLT). The distribution of SOREMPs throughout the MSLT has not been systematically studied in narcolepsy. An uneven occurrence of SOREM throughout the day could influence the diagnostic resolution of the test in narcolepsy, particularly when using short MSLT versions. We studied the temporal distribution of SOREMPs in the MSLT of a large series of narcoleptics and the diagnostic value of the three and four- nap versions of the test. One hundred and twenty-nine patients consecutively diagnosed with narcolepsy underwent nocturnal polysomnography followed by a five-nap MSLT. Four hundred and twenty-nine SOREMPs were recorded in 645 MSLT naps (66.5%). The probability of presenting SOREMPs in the fourth nap (3:30 pm) was significantly lower than in the remaining four naps: 22.4% SOREMPs in the first nap, 20.5% in the second, 20.5% in the third, 16% in the fourth and 20.5% in the fifth nap ( p < 0.034). Shortening the MSLT to three or four naps decreased the capability of the test to support the diagnosis of narcolepsy 2 or more SOREMPs in 14.7% and 10% of the patients, respectively. The temporal distribution of SOREMPs in the different naps of the MSLT is not even in narcolepsy, with the fourth nap having the lowest probability of presenting a SOREMP. This should be taken into account when evaluating the results of the MSLT, and particularly when using shorter (three or four nap) versions of the test. This work is not an industry supported study. Dr. Sansa, Salamero, Iranzo and Santamaria indicate no conflicts of interest and nothing to disclose financially. Dr. Falup-Pecurariu was supported through an European Neurological Society fellowship research project.