Dorsal Interosseous Muscle Weakness from Mid-palm Ganglion Cyst.

Ulnar nerve compression is commonly seen at the elbow at the cubital tunnel and the wrist at the Guyon canal but is rarely seen in the hand. This case report describes an 18-year-old male presenting with seven months of atraumatic hand weakness and atrophy associated with heavy weightlifting. Exam demonstrated isolated interosseous muscle atrophy mostly sparing the abductor digiti minimi with intact sensation and negative nerve compression tests including Tinel at carpal and ulnar tunnels, Froment sign, Wartenberg test, cross finger test, and Spurling test. Electromyography and nerve conduction studies demonstrated prolonged distal latency, low amplitude potential, and large amplitude fibrillations with severely reduced motor unit firing in the first dorsal interosseous muscle consistent with ulnar nerve deep motor branch compromise. Magnetic resonance imaging revealed a ganglion cyst between the third metacarpal shaft and the flexor profundus tendon. Given the progressive symptoms, ganglion cyst excision and ulnar motor nerve branch neurolysis were performed.