What is the role of postradiation motor neuron disease and plexopathy in the etiology of focal muscular atrophy (FMA)?

Updated: Feb 20, 2018
  • Author: Sridharan Ramaratnam, MD, MBBS; Chief Editor: Helmi L Lutsep, MD  more...
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Postradiation motor neuron disease and plexopathy

  • This syndrome, which is due to degeneration of lumbar or cervical motor neurons, occurs months to years after irradiation of the neck, abdomen, or pelvis for malignant disease.

  • Muscle atrophy, fasciculations, weakness, and areflexia in the legs may progress rapidly.

  • The syndrome occurs in about 2-10% of susceptible patients, especially in patients who receive more than 3.3 Gy to the spinal cord. It results from vascular damage and white matter necrosis in the spinal cord.

  • In postradiation plexopathy, patients develop asymmetric and often painless muscle weakness and atrophy.

  • EMG findings include characteristic spontaneous myokymic discharges from involved muscles.

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