Post-Radiation Lower Motor Neuron Syndrome

Objective: To describe the clinical features of four patients we encountered with post-radiation lower motor neuron syndromes and to review the related literature. Background: Radiation therapy for malignant neoplasms has been associated with a post-radiation lower motor neuron syndrome (PRLMNS). The earliest descriptions date back to World War II. Methods: We evaluated four patients who developed a lower motor neuron syndrome several years after the completion of radiation therapy to treat malignancies. The clinical and electrophysiological features of these patients are described. Results: Our patients with PRLMNS developed weakness, muscle atrophy, loss of reflexes, and fasciculations in myotomal distributions that corresponded to the regions that had been exposed to radiation. The mean time between radiation exposure and onset of motor symptoms was 14 years. Sensory symptoms were either absent or minor. Motor and sensory nerve conduction studies were normal or only mildly affected. Needle electromyography showed varying degrees of active and chronic denervation changes, primarily in the distributions that had received radiation. Magnetic resonance imaging of the spine and myelography were unremarkable. Serum creatine kinase levels were elevated in two patients. The patients followed a stable to slowly progressive course at a mean follow up of 6.5 years. Conclusions: Patients presenting with lower motor neuron syndromes should be questioned about prior radiation exposure. A diagnosis of PRLMNS carries a relatively favorable prognosis when compared with amyotrophic lateral sclerosis, another acquired motor neuron disorder.