Monomelic amyotrophy

Monomelic amyotrophy (MMA), is a 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 (average age of onset, 15- to 25-year-old). MMA is reported most frequently in Asia but has a global distribution. It is typically marked by insidious onset of muscular 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 associated with MMA. MMA is not believed to be hereditary. Monomelic amyotrophy (MMA), is a 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 (average age of onset, 15- to 25-year-old). MMA is reported most frequently in Asia but has a global distribution. It is typically marked by insidious onset of muscular 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 associated with MMA. MMA is not believed to be hereditary. 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. In terms of the signs and symptoms that are consistent for an individual who has monomelic amyotrophy are the following (although this does not reflect a complete list): Initially most people notice weakness in one hand; they may feel contracture of middle and ring finger and notice a thinning of the subdigital palm of the affected fingers. Progress of the condition varies, and weakness in the arm ranges from minimal to significant. Fasciculations are uncommon (>20%); increased weakness under cold conditions is commonly reported (cold paresis). The disability originates with impaired functioning of the anterior horn cells of the lower cervical cord (lower neck), but the cause of the decline is not fully understood and is still considered unknown. Researchers, including Hirayama, believe that 'forward displacement of the cervical dural sac and compressive flattening of the lower cervical cord during neck flexion' is the contributing factor. Studies consistently note a loss of normal neck curvature (the cervical lordosis) and compression of the cervical chord by the dural sac in forward flexion. A familial link has been found in a minor percentage of cases, including parent-child and sibling-sibling. Because of the unusual distribution of the disease, some researchers speculate that there could be an ethnic link. The condition presents almost exclusively in 15 to 25 year old adults experiencing weakness in hand and arm. A patient history and a neurological exam narrows down the possible diagnosis; this preliminary exam typically includes strength and reflex tests. Cold paresis (increased weakness in cold weather) is reported by most patients (> 80%). Fasciculations are reported as uncommon (< 20%) to common; larger tremors are more consistently cited. Males are far more likely to be diagnosed with the condition.