Postirradiation localized cramp-fasciculation syndrome.

Radiation plexopathy produces numbness, weakness, and reflex changes.1 Excess motor unit activity (EMUA) after irradiation manifests as myokymia and neuromyotonia in affected muscles.2,3 A 65-year-old woman presented with a pulling sensation in the left axilla and intermittent depression of the left arm of 3 to 4 months duration. Ten months earlier she had completed chemotherapy and radiation therapy after a simple mastectomy for breast carcinoma 3 years earlier. On examination, frequent (2 to 3 per minute) intermittent rhythmic contractions of the left latissimus dorsi and pectoralis major muscles were seen (figure 1) (see also accompanying video). The duration of contractions ranged from 3 to 60 seconds during which her left arm was adducted and depressed and an accessory posterior axillary fold was created. No fasciculations or myokymia were observed. Nerve conduction studies showed conduction blocks in the left median and ulnar nerves across Erb’s point. Needle EMG demonstrated rhythmic cramp discharges and occasional fasciculation potentials in the left latissimus dorsi, teres major, and pectoralis major muscles (figure 2). No myokymic, neuromyotonic, or fibrillation potentials were seen. MRI of the brachial plexus and cervical spinal cord were normal. The lack of pain, conduction blocks on nerve conduction study,1 and cramp-fasciculation potentials in muscles within the radiation field suggested a diagnosis of post irradiation rhythmic muscle cramp-fasciculation disorder.