Hirayama disease, also known as monomelic amyotrophy (MMA),[1][2] is a rare motor neuron disease first described in 1959 in Japan. Its symptoms usually appear about two years after adolescent growth spurt and is significantly more common in males, with an average age of onset between 15 and 25 years. Hirayama disease is reported most frequently in Asia but has a global distribution. It is typically marked by insidious onset of muscle atrophy of an upper limb, which plateaus after two to five years from which it neither improves nor worsens. There is no pain or sensory loss. It is not believed to be hereditary.[3][4][5][6]
Both the names for the disorder and its possible causes have been evolving since first reported in 1959. It is most commonly believed the condition occurs by asymmetrical compression of the cervical spinal column by the cervical dural sac, especially when the neck is flexed. However, the disease is uncommon and diagnosis is confused by several atypical reports.[7][8][9]
^Liewluck, Teerin; Saperstein, David S (November 2015). "Progressive Muscular Atrophy". In Dimachkie, Mazen M.; Barohn, Richard J. (eds.). Motor Neuron Disease, An Issue of Neurologic Clinics. Elsevier Health Sciences. p. 766. ISBN9780323413459.