ELECTRODIAGNOSIS OF DEEP PALMAR ULNAR NEUROPATHY AT THE PISOHAMATE HIATUS

We present the clinical and electrophysiological findings of four pati ents with distal ulnar nerve lesions affecting, selectively, the deep palmar branch at the pisohamate hiatus. All presented with hand weakne ss and wasting, sparing the hypothenar muscles, without sensory manife stations. Two had palm pain. Three had possible precipitating trauma t o the hand. All improved: three following decompression of constrictin g bands at the pisohamate hiatus and one spontaneously. At diagnosis, the ulnar motor amplitudes recording first dorsal interosseus (Ist DI) were absent or very low. Recording the abductor digiti minimi (ADM), the amplitudes were normal or borderline. Needle EMG showed fibrillati ons and loss of motor unit potentials in all ulnar-innervated muscles in the hand, except the ADM. Follow-up ulnar conduction studies showed significant improvement of amplitudes recording Ist DI. Based on our cases and analysis of the literature, we conclude that lesions of the deep palmar branch of the ulnar nerve, distal to the branch to the ADM , are frequently caused by compression at the pisohamate hiatus, secon d only to compression by a ganglion. When treated surgically, this dis order carries good prognosis.