Ulnar conduction block at the wrist.

Two cases of ulnar nerve lesions at the wrist are reported. The lesions had an acute onset and exclusively impaired the ulnar motor deep branch. The coexistence of carpal tunnel syndrome in each case allowed an early diagnosis but was somewhat misleading. In both cases, the use of classic motor and sensory conduction studies did not provide clear abnormalities that would have precisely determined the site of the nerve lesion. In both cases, only palmar stimulation of the ulnar motor deep branch showed an important conduction block. This electrodiagnostic finding showed definitively the site of the ulnar nerve lesion at the wrist and excluded proximal ulnar nerve lesions or C8-T1 radiculopathy. In both cases recovery occurred without surgery.