Strained face during sleep in multiple system atrophy: not just a bad dream.

Study objectives: Patients with Parkinson's disease and multiple system atrophy may be subject to sleep state dissociation. Motivated by the fortuitous observation of prominent facial muscle activity during video-polysomnography in patients with multiple system atrophy, we assessed facial motor activity and chin muscle tone during sleep in multiple system atrophy compared to Parkinson's disease and controls.

Methods: A sleep expert blinded to pathology and sleep stage retrospectively analyzed facial activity in 62 video-polysomnography (11 multiple system atrophy, 38 Parkinson's disease, and 13 controls). Facial movements were classified into six categories: "Eyes closing/opening," "Eyebrows frowning," "Raising eyebrows," "Smiling," "Other mouth movements," and "Strained face," an expression involving both the superior and inferior parts of the face. Chin electromyography activity was quantified during Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM) sleep using the atonia index, a validated algorithm.

Results: Multiple system atrophy patients had an increased number of all facial movements compared to controls during NREM. "Strained face" was significantly more frequent in multiple system atrophy compared to Parkinson's disease, even after adjusting for the presence of REM sleep behavior disorder (RBD). Atonia index was lower in multiple system atrophy compared to controls and Parkinson's disease during REM and NREM sleep. This difference remained significant compared to Parkinson's disease in NREM sleep during N1 and N2 after adjusting for the presence of RBD.

Conclusions: Facial movements during sleep are frequent in multiple system atrophy, "strained face" appears to be a hallmark of this condition. The presence of increased facial activity and elevated muscle tone during all stages of sleep in multiple system atrophy may be a manifestation of sleep state dissociation, reflecting more severe neurodegeneration.