A Portuguese case of Hirayama disease.

Hirayama disease, also known as monomelic amyotrophy or juvenile spinal muscular atrophy of the distal upper extremity features the impairment of the anterior horn cells of the distal cervical spinal cord secondary to dural sac anterior displacement during cervical flexion. We describe a case of a 17-year-old boy with a history of scoliosis, evaluated in the emergency department for decreased muscle strength and atrophy of the left upper limb with progressive worsening for about 6 months. We performed electrophysiological studies that showed severe neurogenic atrophy involving the C7–T1 left myotomes. Brain and spine MRI performed showed flattening of the lower cervical cord and dura mater anterior displacement during cervical flexion. These findings were consistent with the diagnosis of Hirayama disease.