Single-fiber electromyography in hyperCKemia: the value of fiber density

Although persistently raised serum creatine kinase (sCK), or hyperCKemia, is considered the biological hallmark of neuromuscular diseases, pauci- or asymptomatic- or isolated-hyperCKemia can often be found. Single-fiber electromyography (SFEMG) is an electrophysiological technique of great value in the assessment of neuromuscular, neuropathic and myopathic disorders. We hypothesize that SFEMG fiber density (FD) evaluation is able to detect subclinical electrophysiological abnormalities indicating a myopathic process in subjects with hyperCKemia. Nineteen subjects with hyperCKemia without evident clinical signs of muscle involvement and 15 healthy controls were studied. Electrophysiological investigations including nerve conduction studies (NCS), quantitative EMG (QEMG), SFEMG with focus on FD measurements, and muscle biopsy were performed. NCS, QEMG, SFEMG were normal in all controls. In subjects with hyperCKemia, NCS were normal; QEMG was abnormal in 5, while both SFEMG and muscle biopsy disclosed abnormalities in 12 subjects. The mean FD value was 2.6 ± 0.5 in the control and 4 ± 1.4 (p = 0.003) in the hyperCKemia group. SFEMG revealed subclinical changes in the majority of subjects with hyperCKemia. To the best of our knowledge, this is the first study demonstrating that SFEMG FD evaluation is able to detect the presence of muscle diseases, which are in a subclinical phase and would remain unidentified otherwise. SFEMG may be used to distinguish hyperCKemia associated to asymptomatic muscle disorders from idiopathic hyperCKemia. We believe that SFEMG FD evaluation should be added to the routine examinations in the screening of idiopathic hyperCKemia.