Release: Immediate

Contact: Kenneth Satterfield561-447-5521 (May 9-14, 2002)


A study finds that procedures to preserve nerve integrity may not prevent voice problems after removal of the thyroid.

Boca Raton, FL -- Nerve damage resulting from thyroid surgery is a feared consequence of the procedure. Damage to the recurrent laryngeal nerve, which powers the vocal cords, may occur without symptoms, leading some thyroid surgeons to examine the vocal folds preoperatively, and to perform fiberoptic laryngoscopy as part of postoperative follow-up. Injury to the superior laryngeal nerve is another voice-altering complication of thyroid surgery. The associated symptoms of superior laryngeal nerve injury can be nonspecific, and the subtle laryngoscopic manifestations are often overlooked. Advanced diagnostic techniques for evaluating superior laryngeal nerve function have been developed, recording a five to 28 percent incidence of this complication following thryoidectomy. The absence of effective treatment for superior laryngeal nerve palsy and the fact that recovery following nerve injury is poor makes prevention crucial.

Preservation of recurrent and superior laryngeal nerve integrity is important in sustaining vocal capability and function; yet, not all voice alterations following thyroidectomy are related to injury of these nerves. In fact, voice disturbances have been demonstrated in cases where the laryngeal nerves have been preserved, and have been attributed to surgical trauma and laryngotracheal fixation of the pre-laryngeal strap musculature . One study documented vocal fold changes in five percent of patients following endotracheal intubation alone. Some post-operative voice changes may be attributable to arytenoids trauma sustained during tracheal intubation.

The history of post-thyroidectomy voice disturbances for patients with preserved nerve function has not been systematically studied, and its characterization is important for rehabilitation, particularly in professional voice users. A team of researchers has conducted a prospective evaluation of patients undergoing thyroid surgery to characterize the changes in voice that occur following thyroidectomy for patients with normal pre-operative voice.

Authors of the study, "A Prospective Functional Voice Assessment in Patients Undergoing Thyroid Surgery," are Alexander Stojadinovic MD, Ashok R. Shaha MD, Aviram Nissan MD, Bhuvanesh Singh MD, Jay O. Boyle MD, Jatin P.Shah MD, Murray F. Brennan MD, and Dennis H. Kraus MD, from the Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, NY; Robert F.Orlikoff, PhD, from the Communication Sciences Program Hunter College of the City University of New York, New York, NY, and Mary-Frances Kornak MPH, at the Department of Clinical Investigation, Biostatistics Section, Walter Reed Army Medical Center, Washington, DC. Their findings will be presented May 11, 2002, at the Annual Meeting of the American Head and Neck Society, at the Boca Raton Resort & Club, Boca Raton, FL.

Methodology: This was a prospective single-arm study of patients 18 years of age and older with benign and malignant thyroid pathology scheduled to undergo primary thyroid surgery. The study was conducted between September 2000 to April 2001. Eligible patients had no history of professional voice training, had no prior voice pathology requiring therapy, nor previous neck surgery. Patients were ineligible if they had previously undergone neck or thyroid surgery or had isthmusectomy only or radical lymphadenectomy at the time of surgery. Patients with known dysphonia, vocal fold paralysis, history of speech disorder, the inability to sustain phonation for longer than two seconds, those with hearing impairment, or those with anaplastic or medullary carcinoma of the thyroid were excluded.

Functional voice assessment: Voice testing was conducted pre-operative and one week and three months after thyroidectomy. A multidimensional approach to voice analysis was conducted at each visit.

Clinical examination: Pre- and post-operative assessment of voice included the patient and physician's appraisal of voice. The degree of dysphonia was evaluated for grade, roughness, breathiness, and asthenic and strained quality of the voice. Changes of voice pitch, range, intensity, fatigability, and singing quality were assessed during an interview.

Additional testing: Acoustic Testing (vocal flexibility and stability) was performed with a Kay Elemetrics Computer Speech Lab System (4300B), software, Multidimensional Voice Program (MDVP). Vocal capacity was measured by the maximum phonation time (MPT), a measure of the patient's ability to regulate the ventilatory and laryngeal systems for voice production independent of a frequency or intensity target. Detailed appraisal of vocal stability was achieved with frequency-based voice measures including mean vocal fundamental frequency (F0, Hz), F0 variability, mean percent vocal jitter and shimmer, and noise-to-harmonics ratio (NHR, dB). Electroglottography (EGG) was used to provide an accurate assessment of vocal fold pattern of vibration and regularity and degree of vocal fold contact. Vocal fold imaging was conducted with laryngeal videostroboscopy, real-time direct assessment of the symmetry of vocal fold abduction and vibration, the amplitude and regularity of vocal fold movement, traveling (mucosal) wave characteristics, as well as glottic closure and configuration.

Surgery: All patients underwent partial (lobe/isthmus), subtotal, or total thyroidectomy as indicated by the primary pathology, under general endotracheal anesthesia; unilateral or bilateral identification and dissection of the recurrent laryngeal nerve(s) were performed for unilateral thyroid lobectomy; and total thyroidectomy, respectively. The surgeon in all cases of thyroid lobectomy and total thyroidectomy identified unilateral and bilateral recurrent nerves, respectively. The superior thyroid vessels were ligated individually on the thyroid capsule in an effort to avoid injury to the external branch of the superior laryngeal nerve (EBSLN). When the EBSLN could not be readily identified, no further dissection was pursued, to avoid inadvertent nerve injury.

Patterns of change from baseline to postoperatively were evaluated using repeated measures analysis of variance with each patient serving as his or her own control and to identify trends. Changes in voice parameters at each time point were compared between patients with and without voice change using the Wilcoxon rank sum test. The analysis of categorical data was conducted using Fisher's exact or Chi squared test where appropriate.

Results: Fifty-four patients were enrolled; 50 and 46 were evaluable at one-week and three-months, respectively. No patient developed recurrent laryngeal damage and one (2 percent) had EBSLN injury. Fifteen (30 percent) patients reported early and seven (14 percent) late (three-month) subjective voice change. Forty-two (84 percent) patients had significant objective change in at least one voice parameter. Six (12 percent) had significant alterations in greater than three voice measures, of which four (67 percent) were symptomatic; whereas, 25 percent with three or less objective changes had voice symptoms. Patients with persistent voice change at three months had an increased likelihood of multiple early objective changes (43 percent vs. 7 percent). Early maximum phonational frequency range (MPFR) and vocal jitter changes from baseline were significantly associated with voice symptoms at three-months. The criteria of >25 percent decrease in MPFR and >100 percent increase in vocal jitter had a sensitivity form long-term voice symptoms of 71 percent and specificity of 91 percent.

Conclusions: The findings reveal that factors other than laryngeal nerve injury appear to alter post-thyroidectomy voice. In this study, early vocal symptoms were common following thyroidectomy, and persist in 14 percent of patients. Multiple (>3) objective voice changes correlated with early and late post-operative symptoms. Alterations in MPFR and vocal jitter predicted late perceived vocal changes. The variability of patient symptoms underscores the importance for those performing thyroid surgery to understand the physiology of dysphonia.

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