Objective:

To compare quantitative REM sleep without atonia (RSWA) across narcolepsy type 1 (NT1), narcolepsy type 2 (NT2), and idiopathic hypersomnia (IH) and evaluate diagnostic discrimination.

Background:

RSWA is the electromyographic hallmark of REM sleep behavior disorder and occurs in over half of patients with narcolepsy, where it is postulated to reflect hypocretin deficiency. The degree of RSWA among NT1, NT2, and IH has not been systematically compared in adults.

Design/Methods:

We retrospectively analyzed 77 adults (20 NT1, 25 NT2, 32 IH) without antidepressant use who underwent polysomnography (PSG) followed by multiple sleep latency testing (MSLT) at our sleep center from 2022-2024. RSWA was quantified on mentalis and flexor digitorum superficialis EMG as percent REM epochs with excessive muscle tone based on the definition in AASM scoring manual version 3.

Results:

Median RSWA was 2.5%[0.12%, 3.7%] in NT1, 0%[0%,3%] in NT2, and 0%[0%,1.6%] in IH (p = 0.028). In age- and sex- adjusted regression, RSWA was significantly greater in NT1 compared with NT2 (rate ratio = 0.36, 95 % CI 0.14–0.95, p = 0.039) and IH (rate ratio = 0.13, 95 % CI 0.05–0.35, p < 0.001). IH also showed lower RSWA than NT2 (rate ratio = 0.37, 95 % CI 0.14–0.93, p = 0.035). Higher RSWA was correlated with higher percentage of PSG REM sleep (p-value 0.019), shorter PSG and MSLT sleep latency (p-value 0.037, 0.004), shorter MSLT REM sleep latency (p-value<0.001) and higher total MSLT sleep onset REM periods (p-value 0.040). An RSWA cut-off ≥ 2.8% predicted dream enactment in NT1 and NT2 with AUC = 0.81 with sensitivity of 77% and specificity of 85%.

Conclusions:

RSWA quantity is highest in NT1, intermediate in NT2, and lowest in IH and may serve as an adjunct PSG marker of narcolepsy.