Clinical and laboratory findings of 21 patients with radiation-induced myopathy

Background Limited data are available on radiation-induced myopathy (RIM) in adult cancer survivors. Methods We retrospectively reviewed the clinical, electrophysiological, serological, radiological and pathological findings of patients with RIM seen in the neurology clinic over a 11-year period (2002-2013). Results Out of 251 patients with radiotherapy-induced neuromuscular complications, 21 had RIM (11 men and 10 women). Cancers included: Hodgkin's lymphoma (13), non-Hodgkin's lymphoma (one), pinealoblastoma (one), tongue (two), nasopharyngeal (one), thyroid (one) and testicular cancer (two). Various radiotherapy protocols were used but all patients received neck and upper torso radiation. The mean latency between radiation exposure and onset of RIM was 15 years (range 2-45 years). The most common presentation was head drop (43%) followed by neck pain (38%). Axial (86%) and periscapular (81%) muscle weakness and atrophy were frequent findings. Two patients died in follow-up from hypercapnic respiratory failure secondary to neuromuscular weakness. Serum creatine kinase values were usually normal or slightly elevated. EMG revealed predominantly myopathic changes in the axial and periscapular muscles. Half of the muscle biopsies (6/12) showed myopathic changes; increased connective tissue elements were observed in seven of eight muscle biopsies performed in the irradiated field; and mitochondrial dysfunction in two. Conclusions RIM is a potential long-term neuromuscular adverse effect of radiation exposure in Hodgkin's disease and other types of cancer manifesting predominantly as head drop and can be fatal due to neuromuscular respiratory failure. Improved radiotherapy protocols might reduce the risk of RIM and other radiation-induced neuromuscular complications.