Monomelic amyotrophy

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Monomelic amyotrophy (MMA), also known as Hirayama disease, Sobue disease, juvenile non-progressive amyotrophy and juvenile asymmetric segmental spinal muscular atrophy (JASSMA) — is an untreatable, focal motor neuron disease that primarily affects young (15- to 25-year-old) males in India and Japan. MMA is marked by insidious onset of muscular atrophy, which stabilizes at a plateau after two to five years from which it neither improves nor worsens. There is no pain or sensory loss associated with MMA. Unlike other lower motor neuron diseases, MMA is not believed to be hereditary and fasciculations (involuntary muscle twitches) are rare.

EMG tests reveal loss of the nerve supply, or denervation, in the affected limb without conduction block (nerve blockage restricted to a small segment of the nerve). Increased sweating, coldness and cyanosis have been reported for a few patients, indicating involvement of the sympathetic nervous system.

While MMA will cause weakness and/or wasting in only one limb, EMG and NCV tests often show signs of reinnervation in the unaffected limbs.


There is no cure for MMA. Treatment consists of muscle strengthening exercises and training in hand coordination. It has been proposed that the changes in this disease are from compression of the spinal cord in flexion due to forward shifting of the posterior dural sac.[1] There have been treatments studies ranging from use of a cervical collar[2] to anterior cervical fusion and posterior decompression.[3]


The symptoms of MMA usually progress slowly for one to two years before reaching a plateau, and then remain stable for many years. Disability is generally slight. Rarely, the weakness progresses to the opposite limb. There is also a slowly progressive variant of MMA known as O'Sullivan-McLeod syndrome, which only affects the small muscles of the hand and forearm and has a slowly progressive course.


MMA mostly occurs in males between the ages of 15 and 25. Onset and progression are slow. MMA is seen most frequently in Asia, particularly in Japan and India; it is much less common in North America.


  1. ^ Lai V, Wong YC, Poon WL, Yuen MK, Fu YP, Wong OW (December 2011). "Forward shifting of posterior dural sac during flexion cervical magnetic resonance imaging in Hirayama disease: an initial study on normal subjects compared to patients with Hirayama disease". Eur J Radiol (primary source). 80 (3): 724–8. doi:10.1016/j.ejrad.2010.07.021. PMID 20727701. 
  2. ^ Hassan KM, Sahni H (2013). "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective". Biomed Res Int. 2013: 478516. doi:10.1155/2013/478516. PMC 3770029Freely accessible. PMID 24063005. 
  3. ^ Lin MS, Kung WM, Chiu WT, Lyu RK, Chen CJ, Chen TY (June 2010). "Hirayama disease". J Neurosurg Spine. 12 (6): 629–34. doi:10.3171/2009.12.SPINE09431. PMID 20515348. 

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