November 13, 2015: Hirayama Disease

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November 13, 2015

Hirayama Disease

Monomelic amyotrophy, also known as Hirayama Disease, is a rare form of focal motor neuron disease characterized by an initially progressive wasting of the intrinsic muscles of the hands and forearms that becomes stable within a few years. Those affected are typically young males, in their teens through early 30s, and the etiology is due to a tight dura that allows for compressive flexion injury to the C5 through T1 anterior horn cells.

Symptoms include unilateral weakness in one or more myotomes in the absence of upper motor neuron signs. Diagnosis is made via cervical MRI in the flexion position as well as EMG. MRI can show cord atrophy, forward displacement of the dura with the highly sensitive and specific sign of posterior epidural space enlargement. EMG shows fibrillation potentials at affected levels, sometimes bilaterally despite clinical involvement of only one side.

  1. Tavee JO, Levin KH. Myelopathy Due to Degenerative and Structural Spine Diseases. Continuum 2015; 21: 52–66.
  2. Barohn RJ. Clinical Spectrum of Motor Neuron Disorders. Continuum Lifelong Learning Neurol 2009; 15(1).

Submitted by Sarah Wesley, MD, Department of Neurology, Mount Sinai Beth Israel Medical Center.

Disclosures: Dr. Wesley is a member of the Resident and Fellow Section of Neurology.

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