It twitches without kicking - An association between fragmentary myoclonus and arousal?

OBJECTIVE

Fragmentary myoclonus (FM) is a polysomnographic motor phenomenon of unknown clinical relevance. This study investigates FM prevalence, gender differences, sleep stage distribution and association with clinical factors using recently introduced advanced FM scoring criteria.

METHODS

We analyzed polysomnographic recordings of 178 patients of a mixed sleep-disorder patient cohort. FM indices (FMI) of newly introduced 25 μV (FMI25) and standard 50 μV (FMI50) amplitude cut-offs were calculated.

RESULTS

FMI25 and FMI50 were higher in men compared to women. FMI were higher during wakefulness and lower during S3 compared to all other sleep stages, with stronger effects in men compared to women. FMI25 was correlated with higher age, lower mean oxygen saturation, lower sleep efficiency, higher periodic limb movement (PLM) index, shorter sleep period time and higher arousal index. Linear regression showed that age predicted higher FMI25 in both males and females. Additionally, higher arousal index predicted higher FMI25 in women only. FMI were not associated with the presence of sleep-related breathing disorders.

CONCLUSIONS

We suggest FM represents a ubiquitous motor phenomenon occurring spontaneously during relaxed wakefulness and sleep, primarily in men and with advanced age.

SIGNIFICANCE: In women, particularly FMI25 may be a surrogate marker for more frequent arousals and sleep fragmentation.