Pediatric Hirayama disease.

We report on a 16-year-old girl with muscular atrophy of a distal upper extremity (Hirayama disease). The disease progressed insidiously, and during our first examination, she exhibited weakness and wasting in the right hand, accompanied by cold paresis. No sensory disturbance was evident. A nerve conduction test revealed reduced compound muscle action potential of the ulnar and median nerves of the affected hand. However, conduction velocities were normal. An F-wave test of the right ulnar nerve indicated reduced frequency and prolonged minimum latency. Magnetic resonance imaging of the cervical spinal cord demonstrated abnormal signal intensity in the anterior horn, atrophy in the lower cervical cord, a forward shift of the lower cervical cord upon neck flexion, and flow voids in the epidural space. These clinical findings are typical of Hirayama disease. The use of a cervical collar did improve the patient's hand strength after 2 years. Pediatric neurologists should be aware of this disease, particularly in its early course, to diagnose it early, and to introduce a neck cervical collar as soon as possible after diagnosis.