Risk factors:
(1) high total radiation dose (> 6,000 Gy)
(2) high radiation dose fraction (>= 200 Gy)
(3) concurrent cytotoxic chemotherapy
Onset is months to years after the radiation therapy. It tends to be progressive but may plateau after several years.
Clinical features:
(1) Pain is not prominent.
(2) Limb swelling with or without clinical lymphedema may be present.
(3) Weakness in the upper extremity may be present, especially in muscles supplied by the upper roots (C5, C6)
(4) Paresthesias of the upper extremity may be present.
(5) EMG shows myokymic discharges (spontaneous groups of action potentials that are followed by a period of silence)
Differential diagnosis:
(1) tumor invasion of the brachial plexus (severe pain and/or Horner syndrome may be distinguishing features)
