Outcome of Tendon Transfer for Monomelic Amyotrophy (Hirayama Disease).

Hirayama disease is a motor neuron disease predominantly affecting adolescent males. The identifying feature of Hirayama disease is unilateral forearm and intrinsic muscle weakness that spares the brachioradialis, termed "oblique atrophy." Hirayama disease progresses slowly over several years, followed by an abrupt arrest. The pathognomonic finding is the anterior displacement of the cervical spinal cord with the detachment of the posterior dura. Systematic clinical evaluation and appropriate diagnostic studies are crucial to rule out a variety of compressive, immune-mediated, and genetic disorders. We present a patient with Hirayama disease whose hand function was improved dramatically by a tendon transfer after nearly 3 years without a definitive diagnosis and call attention to the hand surgeon's role in identifying this rare disease to enable timely functional restoration.