Though Hirayama disease is self-limiting, early diagnosis is still necessary, because placement of a cervical collar will prevent neck flexion, which has been shown to stop disease progression. The preferred surgical procedure for these patients is anterior spinal decompression and/or fusion with or without duroplasty (8, 9).

Clinically, this potentially treatable condition must be differentiated from conditions that also cause localized amyotrophy of the distal arm—including syringomyelia, motor neuron disease, amyotrophic lateral sclerosis, cervical spondylotic myelopathy, and spinal cord tumor.

While a diagnosis of Hirayama disease is straightforward at flexion MR imaging, the challenge for the neuroradiologist is to identify this condition on routine non-flexion MR
studies.

From our series, we found that asymmetric cord compression is one of the most characteristic findings of this disease, both clinically and radiologically. Thus, in cases of adolescent onset distal upper limb weakness, the finding of asymmetric cord atrophy on routine non-flexion MR studies, especially at the lower cervical cord, should raise the suspicion of Hirayama disease. When this sign is seen, a flexion MR study should be performed to confirm the diagnosis.