Abstract
We conducted nerve conduction studies (NCSs) of the ulnar nerve in 10 patients with Guyon canal syndrome. In three patients, the distal latency (DL) of compound muscle action potentials (CMAPs) recorded from the first dorsal interosseous (FDI) muscles was significantly prolonged, whereas that recorded from the abductor digiti minimi (ADM) muscles was normal. These findings indicate deep motor branch (distal to hypothenar muscles) lesions. In one patient, abnormal CMAP findings were detected in the FDI and ADM muscles. These findings indicate deep motor branch (proximal to hypothenar muscles) lesions. In three patients, the results of sensory nerve conduction studies (SCS) performed on the little finger were abnormal, as were CMAP findings in the FDI and ADM muscles. These findings indicate lesions proximal to or within the Guyon canal. In three patients, the SCS results obtained from the little finger were abnormal, whereas those of the dorsal cutaneous branch of the ulnar nerve were normal. These findings indicate superficial terminal sensory branch lesions. Evaluation of CMAPs recorded from the FDI muscle and demonstration of a normal dorsal ulnar sensory response are necessary for site of lesion diagnosis in patients with Guyon canal syndrome.
