JACKSONVILLE, FLA. – Voice quality changes after thyroid surgery are detectable by using both subjective and objective measures, according to investigators at Monash University in Melbourne, Australia.

After thyroid surgery, up to 80% of patients with functional recurrent laryngeal nerves (RLNs) have reported voice changes, so the investigators set out to evaluate the extent of those voice changes and how the extent of the operation and RLN edema may affect them.

“It has been confirmed that thyroid procedures do alter the voice without necessarily causing a measurable recurrent laryngeal nerve palsy,” said lead investigator Dr. James Lee, “and the change of voice is correlated to the extent of surgery and the amount of nerve swelling.” The findings were presented at the Association of Academic Surgery/Society of University Surgeons Academic Surgical Congress.

The study evaluated 62 patients who had total and partial thyroidectomy surgery between 2010 and 2011 at the Monash University Endocrine Surgery Unit. To subjectively measure voice quality after surgery, the researchers used the Voice Disorder Index (VDI), which measures voice quality on a 0-40 scale from best to worst. After surgery, the mean VDI score in this group showed a 5.2 plus or minus 1.2–point deterioration from 4.2 to 9.4 (P less than .001). For objective evaluation, the researchers used the Dysphonia Severity Index (DSI), which scores voice quality on a scale of –5 to 5 from worst to best. After surgery, the mean DSI score showed a 1.1 plus or minus 0.2–point deterioration from 3.9 to 2.8 (P less than .001). Two speech pathologists conducted the voice assessments.

“Subjective scoring of both hemithyroidectomy and total thyroidectomy reported worse voice postoperatively,” Dr. Lee said. “However, when you take a close look at the numbers, those undergoing total thyroidectomy reported a higher measure of deterioration in their voice.”

Patients who had either partial and total thyroidectomy reported significant subjective deterioration of their voice with mean VDI change from 5.4 to 7.9 (P = 0.02) and 3.5 to 10.6 (P less than .001), respectively. However, on objective evaluation, only the total thyroidectomy patients showed significant voice deterioration, with a mean DSI change from 4 to 2.5 (P less than .001).

Dr. Lee noted that study outcomes between partial and total thyroidectomy patients diverged in another respect: the impact RLN swelling had on voice deterioration. To evaluate RLN swelling, the researchers measured the diameter of the nerve with Vernier calipers before and after the lobectomy during each operation. RLN diameter increased 0.58 plus or minus 0.05 mm on average (P less than .001). In patients who had partial thyroidectomy, the greater the RLN swelling, the worse the subjective score (P = .03). This was not the case in the total thyroidectomy patients where involvement of two nerves complicates the interaction, he said.

During follow-up, the investigators came upon a revelatory finding. “With median 8-month follow-up, the self-reported, VDI scores had returned to baseline levels,” Dr. Lee said. “Interestingly, not only did the objective DSI scores show a return to baseline levels, but it exceeded the baseline levels, meaning the voice had scored better after surgery than before.” However, he noted only 13 patients completed the follow-up.

“Voice change post-thyroidectomy without recurrent laryngeal nerve injury is a complex phenomenon and is likely multifactorial, and we only looked at two of those factors: the extent of surgery and the gradient of recurrent laryngeal nerve injury with nerve edema as a surrogate,” Dr. Lee said. Future studies should evaluate other factors, including the role of the external branch of the superior laryngeal nerve and patient factors such as diabetes or smoking, he said.

Dr. Lee and his coauthors had no disclosures.