Monomelic amyotrophy (MMA) is a medical condition in which there is a progressive degeneration and loss of motor neurons. Motor neurons are the nerve cells in the brain and spinal cord that control voluntary muscles. Also referred to as Hirayama disease and juvenile non-progressive amyotrophy, MMA is not considered to be hereditary. Unlike other lower motor neuron conditions, fasciculations (involuntary muscle twitches) are rare.
Symptoms
Focal motor neuron disease primarily affects young (15–25 year old) population. As far as diagnosis goes, EMG tests reveal loss of the nerve supply, or denervation, in the affected limb. Increased sweating, coldness and cyanosis are some of the complaints reported by few patients. 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.
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Treatment and Prognosis
As of now, there is no cure for MMA. The treatment is supportive, involving muscle strengthening exercises and training in hand coordination.
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.
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