The value of electrophysiological examination of the flexor carpi ulnaris muscle in the diagnosis of cubital tunnel syndrome.

In the electrodiagnosis of cubital tunnel syndrome, the abductor digiti minimi (ADM) muscle is frequently used to evoke compound muscle action potentials (CMAP) in order to measure the motor nerve conduction velocity (MNCV) in the ulnar nerve. Slowing of the MNCV across the elbow is a major criteria in the electrodiagnosis of cubital tunnel syndrome. However, in advanced cases, slowing of the MNCV is also seen in the forearm segment, thus, localization of the nerve palsy is sometimes difficult. We evoked CMAP from the flexor carpi ulnaris (FCU) muscle to assess the value of electrophysiological examination of this muscle in the diagnosis of cubital tunnel syndrome. CMAP from the FCU muscle could be evoked in many cases when CMAP from the ADM muscle could not. Also, the motor terminal latency (MTL) of the FCU was prolonged in proportion to the slowing of the MNCV across the elbow. Therefore, electrophysiological examination of the FCU muscle is useful in the diagnosis of cubital tunnel syndrome, especially when intrinsic muscle atrophy is severe and the CMAP from these muscles cannot be evoked.