Sleep-Related Rhythmic Sound From the Vocal Cords: A Possible Atypical Form of NREM Parasomnia.

Sleep-related noises may have different features and etiologies. Here we report an atypical case of an adolescent with episodes of "sleep-related vocalization" occurring every night, especially during the first part of the night. The patient had moderate mental retardation and a dysfunctional dysphonia; she had no recollection of the episodes and complained exclusively of mild excessive daytime sleepiness. A video polysomnography recording documented two typical manifestations during non-rapid eye movement (NREM) sleep, characterized by the persistence of slow waves and without any electroencephalographic or breathing abnormalities. The quantified analysis of the acoustic features while confirming the rhythmic and stable characteristic of the sound suggests the involvement of the vocal fold vibration on its production. We interpreted these episodes as an atypical form of NREM parasomnia. A possible influence of the otolaryngologic abnormality can be hypothesized.