Electrodiagnosis of motor unit disorders.

Electromyography and nerve stimulation studies evaluate the function of lower motor neurons, nerve roots, plexus, peripheral nerves, neuromuscular junctions and muscles. Electrodiagnostic studies differentiate myopathic and neuropathic muscle weakness. No single abnormality is diagnostic for a particular disease. The combination of certain abnormal findings and their pattern of presentation in specific muscle groups, when correlated with the patient's history and clinical findings, will help to identify and localize a lesion in the motor unit pathway.