Assessment of fragmentary myoclonus in healthy sleepers

Abstract

Introduction Fragmentary myoclonus (FM) is characterised by a multifocal synchronic and asymmetric distribution of EMG potentials with a duration of 75–150 msec and an amplitude exceeding 50 μV. The extreme form of FM is excessive fragmentary myoclonus (EFM). The presence of FM has been described in many sleep disorders, its clinical relevance, however, is still under debate. In the International Classification of Sleep Disorders-2 it is therefore listed in the category “Isolated Symptoms, apparently Normal Variants and Unresolved Issues”. The aim of this study was to assess FM in healthy sleepers. Materials and methods One-hundred healthy sleepers (60 f, 40 m) aged 19–77 years were selected from a representative Tyrolean population sample. A two-step screening process (telephone interview, personal investigation by a sleep-trained physician) was performed for exclusion of a relevant sleep, neurological, psychiatric or internal comorbidity as well as any use of a CNS active medication. All participants underwent one video-polysomnography. Analysis of FM was part of the comprehensive analysis of motor phenomena during sleep. It was quantitatively assessed according to Lins et al. EFM was diagnosed according to AASM 2007. Results Every study participant had FM. Median FM index in sleep was 25.3/h [range 3/h–1102/h]. The highest rates were seen in REM 38/h [0/h–1102/h] sleep followed by N1 34.4/h [3/h–1048/h] and N2 22.3/h [1.5/h–1032/h] sleep. The lowest values were found in N3 37.8/h [0/h–1200/h] sleep. Men had higher rates of FM in sleep than women (median of 39.9/h [2.94/h–1032/h] vs. median 20.3/h [0/h–792.7/h]; p Conclusion This is the first study systematically assessing FM in healthy sleepers on a quantitative base. Our data showed that FM was present in every healthy sleeper and is therefore an ubiquitous phenomenon. Of note, men are more frequently affected than women. As the rates of FM increased with age, one might suggest FM a normal physiological phenomenon of aging. Acknowledgements This study was supported by the Austrian Science Fund (KLI 236) for the project “Motor activity during sleep in health and disease” to Birgit Frauscher.