Bell's palsy and the chorda tympani nerve: a clinical and electron microscopic study.

The chorda tympani nerve plays an important role in the pathogenesis of Bell's palsy. The chorda tympani nerve is altered early in the course of the disease, perhaps before involvement of the facial nerve occurs. This was demonstrated by studying the pathophysiologic alterations of the chorda tympani nerves of 15 patients with Bell's palsy. Fifty-seven percent of the patients noted taste aberrations two days before the onset of the facial paralysis. In addition, chorda tympani nerve function, tested by electrogustometry and by determining submandibular salivary flow, was altered before the response to nerve excitability became reduced; further, the electron micrographic findings in two patients indicated that the involvement of the chorda tympani nerve preceded the time of onset of the facial paralysis. The study established a relationship between the pathologic involvement of the chorda tympani nerve and the facial nerve. There was a direct relationship between the severity of changes noted microscopically in the chorda tympani nerve specimens and the ultimate recovery of facial motor function. Examination of the chorda tympani nerve specimens was used to correlate the effectiveness of treatment. The results of steroid therapy and surgical decompression were compared. Steroids had no beneficial effect. Complete return of facial function was associated with surgical management when surgery was performed based on reduced salivary flow to 25 percent of normal and while the response to maximal stimulation was still normal.