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

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. We studied the temporal distribution of SOREMPs in the MSLT of a large series of narcoleptics and calculated the effects of age and the diagnostic value of shorter versions of the test.

129 patients consecutively diagnosed with narcolepsy (73.4% with cataplexy) underwent nocturnal polysomnography followed by a five-nap MSLT.

429 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 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). Patients older than 29 years had less SOREMPs than the younger ones (p:0.045). Shortening the MSLT to three or four naps decreased the capability of the test to support the diagnosis of narcolepsy in 14.7 and 10% respectively.

The temporal distribution of SOREMPs in 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 versions of the test.