ELECTROMYOGRAPHY IN MYOPATHY

Electromyography (EMG) is the most common procedure for screening pati ents with myopathies and remains the most important technique for asse ssing the course of the disease over time. Fibrillation potentials, po sitive sharp waves, myotonic or complex repetitive discharges, as well as polyphasic potentials are non specific and can occur in both myopa thic and neurogenic lesions. The most sensitive and specific parameter for myopathy in conventional EMG is the decreased duration of motor u nit potentials (MUP), but this can also be seen in disorders of the te rminal motor fibers or the neuromuscular junction. More advanced techn iques such as single fiber EMG, macro EMG, scanning EMG and turns/ampl itude analysis have opened additional possibilities for analysis of th e motor unit and the interference pattern, by which both the sensitivi ty to early changes and specificity for myopathic alterations is incre ased. The importance of combining different techniques to improve diag nostic yield and specificity is stressed.