Rupture of the flexor pollicis longus in von Recklinghausen's disease.

An unusual cause of inability to flex the interphalangeal joint of the thumb in a patient with von Recklinghausen's disease is reported. A tumor in the cubital fossa and the basic characteristics of this disease led to a preoperative misdiagnosis of anterior interosseous nerve paralysis. However, surgical exploration and histological examination showed that the correct diagnosis was rupture of the flexor pollicis longus tendon caused by intratendinous proliferation of a neurofibroma. This is the first report in the English-language literature of a flexor tendon rupture caused by intratendinous tumor proliferation.