The significance of pathological spontaneous activity in various myopathies.

ABSTRACT

OBJECTIVE: Pathological spontaneous activity (PSA) in electromyography (EMG) has not yet been systematically analysed in various types of myopathies. METHODS: 136 Patients with well-defined myopathies were retrospectively analysed for the presence of PSA in distal, proximal, and paravertebral muscles. PSA comprised fibrillations (fib)/positive sharp waves (PSW) and high frequency discharges (HFD; i.e., myotonic and complex repetitive discharges). RESULTS: fib/PSW occurred more frequently than HFD. HFD were rarely myotonic in nature. 50% and more patients presented with HFD in PROMM (80%), Pompe's disease (70%), matrin-3 myopathy (60%), sIBM (50%), CNM (50%), while far less than 50% of the patients showed RD in LGMD2I (21%), LGMD2A (17%), LGMD2B (17%), LGMD2L (14%), FSHD (4%), BMD (0%). Four different HFD patterns were proposed. CONCLUSION: The segregation of myopathies relative to the occurrence of PSA and especially HFD in a high prevalence group and in a low prevalence group may be diagnostically valuable. SIGNIFICANCE: The screening for HFD by means of EMG is also valuable in the diagnosis of non-myotonic myopathies.