Acute ulnar neuropathy at the wrist: a case report and review of the literature.

Acute ulnar neuropathy at the wrist is an extremely uncommon condition, at times requiring a high index of suspicion for the diagnosis. Clinical presentations of ulnar nerve lesions at the wrist and hand show variations due to the complex anatomic course of the nerve in distal sites. We report a case of acute ulnar neuropathy at the wrist caused by a ganglion in Guyon's canal, being initially misinterpreted as flexor tenosynovitis. The accurate diagnosis of selective distal motor neuropathy of ulnar nerve was made electrophysiologically. Magnetic resonance imaging revealed a well defined soft tissue mass consistent with a ganglion, compressing the ulnar nerve in Guyon's canal. Entrapment neuropathies are one of the common conditions handled by physiatrists. Ulnar nerve lesions at the wrist should be kept in mind in the differential diagnosis of patients with wrist or hand pain. Magnetic resonance imaging is a useful method in the anatomical evaluation of acute focal neuropathies.