The Chorda Tympani Nerve Role in Taste Impairment in Middle Ear Disease and after Ear Surgery

Berling Holm, K. 2017. The Chorda Tympani Nerve. Role in Taste Impairment in Middle Ear Disease and after Ear Surgery. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1306. 54 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9837-5. The chorda tympani nerve, also known as the taste nerve, runs uncovered through the middle ear cavity, a localization that exposes the nerve to pathological processes and surgical trauma in the middle ear. People operated on for otosclerosis tend to complain more about postoperative taste disturbances than those operated on for chronic otitis media. It has been suggested that this difference may be explained by gradual deterioration of chorda tympani nerve function caused by chronic otitis media infection and that further impairment caused by surgery is less noticeable in these patients. This thesis aimed to evaluate the function of the chorda tympani nerve, the effects of middle ear disease on taste and complications resulting from ear surgery for chronic otitis media or otosclerosis. This information will help to improve the ear surgeon’s ability to predict the prognosis of iatrogenic taste disturbances in patients with middle ear disease and after ear surgery. Taste was assessed using electrogustometry and the filter paper disc method before and after surgery for chronic otitis media or otosclerosis. Patients also completed questionnaires about symptoms and quality of life. The status of the chorda tympani nerve upon surgical opening of the ear and grading of the trauma to the nerve during the surgery were recorded. The ultrastructure of the chorda tympani nerve from healthy ears and from ears with chronic otitis media was examined. Electrogustometry and the filter paper disc method were evaluated. The results of electrogustometry and the filter paper disc method were highly reproducible, although their correlation was moderate. Patients with chronic otitis media, patients with a more traumatized nerve, female patients and younger patients were more likely to report postoperative taste disturbances. Most of the patients recovered their taste after 1 year. The quality of life study showed only minor changes after surgery. Electron microscopic observations of nerves from ears with chronic otitis media showed signs of structural degeneration, although signs of regeneration, such as sprouting were also observed. This results may explain the recovery of taste postoperatively and indicate that the nerve should be carefully handled during surgery.