Incidence of long-term ipsilateral and contralateral ototoxicity following radiotherapy for nasopharyngeal carcinoma

Objective

To characterize the long-term adverse effects of radiotherapy on the ears in patients with nasopharyngeal carcinoma (NPC), we investigated ipsilateral and contralateral ototoxicities in the external, middle, and inner ear.

Methods

The records of 48 ears in 24 radiotherapy-treated NPC patients were retrospectively analyzed. Radiotherapy doses varied between 60 and 70 Gy in 2-Gy fractions at 5 fractions/week. Ototoxicities were identified by otoscope and pure-tone audiograms conducted at 2-3 month intervals for ≥12 months. The relationship between radiation dosage and sensorineural threshold deterioration was statistically compared using the Mann-Whitney U-test.

Results

Post-radiotherapy, 50% of all ears (3 of 6) that developed severe otitis externa were on the contralateral side. There was a post-radiotherapy increase in contralateral otitis media with effusion (OME) (1-7 ears), but a decrease in ipsilateral cases (16-12 ears), with 2 ears on either side subsequently developing chronic otitis media (COM). All ears that showed sensorineural hearing loss (SNHL) before radiotherapy exhibited a further threshold deterioration of more than 15 dB. No statistically significant difference (p = 0.086) in average radiation dose was seen between ears with sensorineural threshold deterioration (50.0 Gy) and those without (48.2 Gy).

Conclusion

Long-term ototoxicity following radiotherapy for NPC can occur in either the ipsilateral or contralateral ears. Pathophysiology varies between and within each side. The post-therapy increase in OME on the contralateral side was thought to be due to radiotherapy-induced Eustachian tube damage, and the sensorineural threshold deterioration in at least 4 ears was thought to be due to chronic cochlea damage secondary to COM.