Hypnic jerks are an underestimated sleep motor phenomenon in patients with parkinsonism. A video-polysomnographic and neurophysiological study

- Hypnic jerks are a frequent and constant video-polysomnographic finding in patients with parkinsonism.
- Hypnic jerks in parkinsonism patients seem to appear early in the disease course.
- Neurophysiological analysis does not show any recurring, ordered propagation pattern of muscle activity during hypnic jerks.
- Hypnic jerks share the same random propagation pattern in both healthy subjects and in patients with parkinsonism.
- The lack of any ordered propagation of the spreading of muscular contraction suggests a subcortical origin of the jerks.

IntroductionHypnic jerks (HJs) are sudden contractions of one or more body segments occurring mostly at sleep onset. They are highly sporadic and affect all ages and both sexes with prevalence between 60% and 70% in the general population.Study objectivesThis study describes the frequency and the neurophysiological characteristics of HJs in a population of patients with parkinsonism by means of nocturnal video-polysomnographic recordings.MethodsThis is a prospective cohort study and is reported following the STROBE guidelines. We analyzed the clinical and video-polysomnographic data of the first 66 consecutive patients recruited in the ongoing prospective study “Bologna motor and non-motor Prospective study on Parkinsonism at onset” (BoProPark). Each patient underwent a full neurological workup including a whole-night video- polysomnography. Neurophysiological characteristics including the propagation patterns of the HJs were studied with an extended muscle montage polysomnography.ResultsWe recorded a total of 62 HJs in 16 patients out of 66 (24%). Sleep parameters were not statistically different between patients with and without HJs. All HJs were spontaneous and occurred randomly throughout the night. Electromyographic analysis showed that muscle activity arose from different muscles with no prevalence of one over the other and without any ordered propagation. No recurring motor pattern of the jerks was detected.Discussion and conclusionsOur findings demonstrated that HJs are a frequent, underestimated, sleep-related motor phenomenon in patients with parkinsonism. As they may represent a further cause of sleep disruption and insomnia, HJs should be actively examined. Neurophysiological analysis suggests a subcortical origin of HJs as shown previously for a healthy subject.