Radial nerve cutaneous innervation to the ulnar dorsum of the hand.

OBJECTIVE: To elucidate the clinical and physiologic features of anomalous superficial radial innervation to the ulnar dorsum of hand.

METHODS: We performed superficial radial and ulnar dorsal cutaneous nerve conduction studies (NCS) in 100 patients without radial or ulnar neuropathy and in 71 patients with various ulnar neuropathies.

RESULTS: Of 100 patients, 16 had anomalous superficial radial innervation to ulnar dorsum of hand. Only 3 subjects had an absent ulnar dorsal cutaneous response without this variant. The anomaly was unilateral in 14 subjects and bilateral in 2, manifesting in 18 of 200 hands (9%). In the 71 patients with various ulnar neuropathies, failure to recognize the variant confounded clinical and NCS diagnoses.

CONCLUSIONS: Anomalous superficial radial innervation to the ulnar dorsum of the hand is the most common cause of an absent ulnar dorsal cutaneous response in the population at large.

SIGNIFICANCE: It is important to recognize this variant to avoid erroneous diagnoses and inappropriate treatment, and to improve assessment of nerve injury and recovery. From a historical perspective, our findings are the first to adequately explain the degree of asymmetry observed by Jabre [Jabre JF. Ulnar nerve lesions at the wrist: new technique for recording from the sensory dorsal branch of the ulnar nerve. Neurology 1980;30:873-6.] in his seminal paper on the ulnar dorsal cutaneous response.