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Isolated REM Sleep Without Atonia

How often have you encountered a handful of incidental epochs with increased chin EMG tone (>50%) while reading a PSG in a patient without clinical symptoms or concern for REM behavior disorder (RBD), and asked yourself any of the following questions: “How common is isolated REM sleep without atonia (RWSA)? Is this worth addressing in the final report? What is the clinical significance of isolated RSWA?” If so, then keep reading, as this study by Feemster et.al. is hot off the press from SLEEP, and answers just these questions!

This study aimed to describe normative RSWA, and characterize isolated RSWA frequency in adults without RBD. 118 adult patients (between 21-88 years of age), seen between 2008 and 2015 at the Mayo Clinic for indications other than reported dream enactment behavior, parasomnia, or sleep-related movement disorders were selected for retrospective RSWA analysis from the polysomnogram (PSG) database. Those with an AHI <15/hour and periodic limb movement index (PLMI) of <15/hour were included for a broad sample that would yield normative levels for RSWA. Phasic and tonic RSWA in the submentalis and anterior tibialis muscles were visually quantified, and the automated Ferri REM Atonia Index (RAI) for the submentalis muscle was also calculated. Isolated RSWA was defined by patients who exceeded the 95th percentile for the overall cohort, and their age-sex deciles, or patients with RSWA levels exceeding previously defined RSWA cutoffs for RBD.

The study found that isolated RSWA elevations (with RSWA exceeding the cohort 95th percentile) were present in 25% of patients, while 14% of patients had sufficient RSWA elevation to fulfill previously established diagnostic cutoffs for RBD RSWA. Additionally, older men had higher RSWA than older women or younger patients (all p < 0.04), suggesting that older men frequently have altered REM sleep atonia control, mirroring the demographic characteristics of RBD.

Prodromal RBD is an evolving concept without a well-established consensus definition. Visual and/or quantitative abnormalities in REM sleep atonia may be used as a plausible biomarker for “prodromal RBD”. However, this will require prospective cohort studies analyzing development of clinical dream enactment and measurement of other degenerative markers for synucleinopathy in order to determine the potential clinical significance of isolated RSWA.

Until then, these data establish normative adult RSWA values, and thresholds for determination of isolated RSWA elevation for use in future studies in patients without dream enactment, potentially aiding RBD diagnosis. Moreover, these data can help guide discussions concerning incidental findings of RSWA during routine clinical polysomnography practice.

(Post by: Vaishnavi Kundel)