Hirayama's disease: the importance of flexion magnetic resonance imaging.

Hirayama's disease is a form of juvenile muscular atrophy affecting young individulas in their second to third decade. The underlying pathogenetic mechanism is believed to be an imbalanced growth between the individuals' vertebral column and the spinal canal contents, which causes abutment of the anterior spinal cord against the vertebral column and detachment of the posterior dura, leading to microcirculatory disturbances and ischemic changes in the cord. This mechanism is exiquisitely demonstrated on magnetic resonance imaging (MRI), but requires additional imaging, with the neck in the flexed position. Neurphysiological imaging studies have provided supporting evidence by demonstrating changes in the N13 potential, with neck flexion. Nonetheless, few studies have also reported contradictory findings with MRI and somatosensory evoked potentials, in Hirayamas Disease. This condition is underdiagnosed because most clinicians are not familiar with this disorder and do not request a flexion MRI. Early recognition of this entity and differentiation from other causes of focal cord atrophy is important, because limitation of neck flexion by using a simple neck collar can prevent its further progression. We report the classical MRI findings in a young patient with Hirayama's disease with neutral and flexion MRI.