Sighs during sleep in multiple system atrophy

Sighs are physiological phenomena and may occasionally occur during sleep in healthy young adults. Although inspiratory sighs are considered a diagnostic red flag for the parkinsonian form of multiple system atrophy (MSA), its frequency and characteristics are unclear. We aimed to define sigh frequency during sleep recordings in patients with MSA compared to Parkinson's disease (PD) patients, as well as evaluate possible associated breathing disorders or autonomic changes. We analyzed 9 polysomnography's from patients with MSA and 9 from matched PD patients. The proportion of MSA patients (both MSA-P and MSA-C) with sleep-related sighs was significantly higher than that of PD patients, and these occurred predominantly in stages N1 and N2. The median sigh index in sleep and wakefulness were also significantly higher in MSA, although with a significant inter-subject variability. Higher sigh indexes were not associated to other breathing disturbances or with longer disease duration. In MSA, 12% of sighs were associated with oxygen desaturation, while none of the events in PD patients presented with significant changes in oxygen saturation. Respiratory events followed 45% of sighs in MSA, predominantly central sleep apneas, and 29% of sighs in PD, predominantly hypopneas. Our data suggests that high sigh frequencies during sleep should also be considered a red flag for MSA, and future studies should aim to determine whether increased sighing frequency during sleep is specific for this disorder.