A longitudinal study of multimodal evoked potentials in patients following radiotherapy for nasopharyngeal carcinoma

Radiation rhombencephalopathy and radiation myelopathy may occur in patients months or years after radiotherapy for malignancy of the head and neck. We obtained multimodal evoked potentials longitudinally in 26 patients with proven nasopharyngeal carcinoma. Recordings were made before radiotherapy and at 1 week, 3 months, 9 months, 15 months, and 24 months after radiotherapy. All absolute latencies of evoked response before and after radiation were within normal limits. However, the I-III interpeak latencies of brainstem auditory evoked potentials and the onset latencies of motor evoked potentials in the whole group of patients at 15 months after radiation were significantly longer than those before radiotherapy, whereas the latencies at 24 months were not significantly different. The N20 latencies of somatosensory evoked potentials after radiotherapy were significantly prolonged at 3 months of follow-up; the prolongation then became normal. They indicate that a subclinical reversible radiation-induced dysfunction may occur in the auditory, sensory, and motor systems.