Electrophysiological pattern of 53 cases of ulnar nerve lesion at the wrist

We aimed to evaluate the relative diagnostic sensitivity and specificity of different motor and sensory conduction electrodiagnostic (EDX) tests used to demonstrate ulnar neuropathy at the wrist (UNW). We also reported some data on associated nerve lesions and unusual causes of UNW.

A prospective case series was conducted in 53 cases of UNW and 100 cases of ulnar neuropathy at elbow (UNE). All cases underwent the same EDX examination according to a protocol defined in 1997. A few cases required additional conduction tests with coaxial needle recording.

The diagnostic sensitivity of the distal motor latency (DML) to adductor digiti minimi (ADM) and sensory conduction was 42% and 19% respectively. The diagnostic sensitivity of the DML to first dorsal interosseous (FDI) was 66% and studying conduction across the wrist to search for conduction block (CB) improved the diagnostic sensitivity up to 90%. In 10% of cases, no EDX test of this protocol allowed locating the site of the UNL. The specificity of each test was 100% for controls, and varied from 100% for conduction block (CB), to 95% (DML to FDI) for UNE. CB at the wrist in UNW was 2.7times more frequent than at the elbow in UNE (57% vs. 22%; P<0.0001). Finally, we found three cases of isolated sensory UNW, 16 of sensory and motor UNW, and 34 of pure motor lesions. A median nerve lesion at the wrist coexisted in 22 cases.

Improving UNW diagnosis requires systematic study of the ulnar motor conduction to FDI across the wrist, and in a few cases conduction tests with a coaxial needle recording.