Absence of multiple sleep-onset rapid eye movement periods (SOREMPs) is not a specific feature of patients with pathological sleep prolongation.

Purpose: Multiple sleep-onset rapid eye movement periods (SOREMPs) are involved in the pathophysiology of narcolepsy, but it is not clear whether the lack of multiple SOREMPs is associated with the pathophysiology of idiopathic hypersomnia or not. We examined the significance of multiple SOREMPs in patients with pathological sleep prolongation.

Methods: Participants were consecutive patients complaining of unexplained sleepiness and agreed to a 3-day-sleep studies; 24 h polysomnography (PSG) followed by standard PSG and multiple sleep latency test (MSLT). Forty-one (26 females, 21.9 ± 8.1 years old, BMI 20.4 ± 2.3 kg/m) of 54 eligible patients without other sleep pathologies showed pathological sleep prolongation. We subdivided them into those with and without multiple SOREMPs on MSLT and compared clinical and PSG variables between groups.

Results: Six of 41 (14.6%) patients showed multiple SOREMPs on MSLT. There were almost no differences in sleep variables between those with and without multiple SOREMPs. We only found shorter mean sleep latency on MSLT and more REM cycles on 24 h PSG in those with multiple SOREMPs (adjusted  = 0.016 and 0.031). The frequencies of REM-related phenomena and clinical symptoms related to idiopathic hypersomnia were not different between groups.

Conclusion: Our results indicated that patients with pathological sleep prolongation had the same clinical profiles regardless of the status of SOREMPs, suggesting the absence of multiple SOREMPs, prerequisite for the diagnosis of idiopathic hypersomnia, is not a specific feature of pathological sleep prolongation. Confirmation of sleep prolongation alone could be a diagnostic tool for idiopathic hypersomnia.