The electromyographic features of acute rhabdomyolysis

Rhabdomyolysis and acute polymyositis share a similar clinical profile with elevated serum creatine kinase (CK). Unlike polymyositis, the electromyography (EMG) findings of acute rhabdomyolysis with myoglobinuria are not well defined. We retrospectively evaluated 15 patients during the acute phase of rhabdomyolysis. All patients (age range, 10-84 years) underwent electrodiagnostic studies, including needle EMG, during the first 2 weeks from the onset of symptoms. All patients presented with acute myalgia, muscle tenderness, and severe generalized weakness. The median peak CK was 48.0 k u/L (25th and 75th percentiles, 11.0 and 68.0 k u/L), whereas the median CK elevation at the time of EMG examination was 10.0 k u/L (25th and 75th percentiles, 4.5 and 48.5 k u/L). Nerve conduction studies were normal in all except 1 patient who had a preexisting mild polyneuropathy. Needle EMG was performed on 117 muscles. Eighty-seven of 117 (74%) muscles were normal, and 19 of 117 (16%) showed variable proximal myopathic motor unit action potentials. None had persistent fibrillation potentials. One third of patients (5 of 15) had myopathic EMG that was present in 1 to 3 sampled proximal muscles. We conclude that the EMG findings during rhabdomyolysis are often normal and when abnormal, the changes are subtle and are in contrast to the often-prominent EMG findings in polymyositis and dermatomyositis.