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

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.

Retrospective review of 102 polysomnographic records.

Sleep laboratory at a University Hospital Neurology Department.

Sixty-two sleep-disorder patients.

None.

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).

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.