Hypersomnolence and narcolepsy; a pragmatic diagnostic neurophysiological approach

Out of a group of 250 consecutive patients who were examined for various disorders of sleep and waking at Ghent University Hospital within a period of 24 months, 30 patients with hypersomnolence associated with a suspected underlying neurological etiology were selected. The population consisted of 15 males and 15 females with mean age of 36 years (range: 16-60 years). Twenty-one patients had had hypersomnolence for more than 2 years. All patients underwent a single night polysomnography (PSG) and a 4-nap multiple sleep latency test (MSLT). PSG was normal in 23 patients. Sleep onset REM period (SOREMP) was defined as the occurrence of REM sleep within 15 min. after initiation of sleep. PSG demonstrated SOREMP's in only 1 patient and showed evidence of obstructive sleep apnea in 4 patients. Two patients had a low sleep efficiency. MSLT demonstrated hypersomnolence in 17 patients of whom 6 showed SOREMP. Significant hypersomnolence was defined as a mean sleep latency < or = 5 min. 4 patients fulfilled the classical clinical and polygraphic criteria (> or = 2 SOREMP) of narcolepsy. In 8 patients the tentative diagnosis of idiopathic CNS hypersomnolence was made. 13 patients did not sleep during MSLT. These results emphasize the relative importance of MSLT. Our limited 4-nap MSLT protocol proved useful in distinguishing narcolepsy from idiopathic CNS hypersomnolence.