Characterized dispersive wave-form of evoked compound muscle action potential in the localized ulnar nerve neuropathy

Disorder of the ulnar nerve with continuity around the elbow is known to be a neuropathy produced by long lasting compression, friction or traction. Forty-four patients with clinical diagnosis of ulnar nerve neuropathy were examined by means of motor nerve conduction study and induced electromyography. Compound muscle action potentials (CMAPs) from hand muscle were evoked by stimulating many points proximal and distal to the elbow and analysis of CMAP was performed. In mild grade of nerve lesion, dispersive wave-form with the extension of its duration was elicited by only stimulating proximal points to the elbow. It was also found that conduction velocity is delayed only over the short distance across the elbow. Thus an initial stage of nerve lesion has a tendency of dysfunctioning of conductivity restricted in only affected portion. CMAP patterns are classified into four groups in comparison with the progress of clinical signs of the disease. This classification can be utilized for the evaluation of the progress of ulnar nerve lesion.