Fragmentary myoclonus in sleep revisited: A polysomnographic study in 62 patients

Abstract

Study objectives To investigate the frequency of fragmentary myoclonus (FM) in a sleep-disorder population, to analyze its distribution across sleep stages and to examine potential associations with clinical correlates and night-to-night variability. Design Retrospective review of 102 polysomnographic records. Setting Sleep laboratory at a University Hospital Neurology Department. Patients Sixty-two sleep-disorder patients. Interventions None. Measurements and results Fragmentary myoclonus (FM) was counted according to published criteria. Sleep stage specific FM indices (FMI) were calculated for each patient. Median FMI was 39.5/h sleep. FMI was the highest in REM sleep, followed by similar indices in wakefulness, S1 and S2 sleep, and was the lowest in S3/S4 sleep (n.s.). FMI increased with age ( ρ = 0.350, P = 0.005). Men had a higher FMI than women (median 55.8/h vs. 24.1/h, P = 0.042). In addition, FMI was positively correlated with the presence of sleep-related breathing disorders ( ρ = 0.270, P = 0.036), respiratory indices (apnea–hypopnea index: ρ = 0.403, P = 0.002; oxygen desaturation index: ρ = 0.378, P = 0.004) and body mass index ( ρ = 0.28, P = 0.028). In a linear regression model, age, male sex and oxygen desaturation index were significant ( P < 0.05). FMI night-to-night variability was 1.6 (range: 1.0–3.9). Conclusion Fragmentary myoclonus was present in every patient of this sleep-disorder population. Its clinical significance is unknown, but the association with oxygen desaturation index points to an association with sleep-related breathing disorders. Since FMI was similar during wakefulness and light sleep, these data challenge the concept of a primarily sleep-related phenomenon.