Two cases of HLA-DR2-negative hypersomnia manifesting sleep-onset rapid eye movement periods in the multiple sleep latency test.

We encountered two cases expressing excessive daytime sleepiness (EDS) and manifesting two or more sleep-onset rapid eye movement (REM) periods in the multiple sleep latency test. Unbearable daytime sleepiness occurred abruptly, which usually led to short-lasting naps, after which the patients felt refreshed. The EDS was successfully reduced by treatment with methylphenidate. In spite of these features similar to narcolepsy, these cases of REM hypersomnia did not present cataplexy or other auxiliary symptoms of narcolepsy, and, furthermore, the class-II human leukocyte antigen DR2 appeared to be negative.