Auditory brain stem responses in patients after radiation therapy for nasopharyngeal carcinoma.

BACKGROUND

The study evaluated the incidence and severity of brain stem myelopathy occurring after radiation exposure in a cohort of patients who received external radiation exposure for nasopharyngeal carcinoma (NPC).

METHODS

Brain stem function was investigated by auditory brain stem responses (ABR).

RESULTS

Four of 21 patients who could be examined had aberrations in ABR. Three patients showed highly abnormal ABR, with no distinctive patterns or peaks. Two of these patients also showed clinical symptoms of brain stem dysfunction, including multiple palsies in cranial and peripheral nerves, whereas the third patient had no clinical signs of brain stem disorders. The fourth patient had minor conduction delays in ABR. The remaining group of 17 patients who could be examined had ABR latency and transmission times similar to those of the control group. None of these patients had neurologic symptoms. Dose-response analysis showed that patients who received radiation doses of 59 Gy or less to the brain stem had normal ABR, whereas four of six patients who received a dose of 68 Gy had manifest or subclinical brain stem dysfunction.

CONCLUSIONS

The results emphasize the importance of protecting the brain stem from high-dose radiation when possible. The results also demonstrate the usefulness of ABR as a supplement to the clinical examination of patients with possible myelopathy occurring after radiation exposure.