Amyotrophy- monomelic

Synonyms

5

Overview

Monomelic amyotrophy (MMA) is an untreatable, focal motor neuron disease that primarily affects young (15- to 25-year-old) males especially 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.

Symptoms

  • Weakness of a single limb
  • Wasting of a single limb
  • No pain
  • Weak hand muscles
  • Weak lower arm muscles
  • Fine motor control problems
  • Weak grip
  • Clawed hand
  • Hand tremors
  • Wasted hand muscles
  • Wasted lower arm muscles
  • Abnormality of the upper limb
  • Asymmetric growth
  • EMG abnormality

Causes

Although the causes of MMA are still to be know, there are few reports which believe that traumatic or radiation injury may be linked to MMA.

Diagnosis

There are also familial forms of MMA. Diagnosis is made by physical exam and medical history. Electromyography (EMG), a special recording technique that detects electrical activity in muscles, shows a loss of the nerve supply, or denervation, in the affected limb; MRI and CT scans may show muscle atrophy. People believed to have MMA should be followed by a neuromuscular disease specialist for a number of months to make certain that no signs of other motor neuron diseases develop.

Prognosis

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

Treatment

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. There have been treatements studies ranging from use of a cervical collar to anterior cervical fusion and posterior decompression.

Resources

  • NIH