Unilateral vocal fold paralysis (UVFP) is a common laryngeal disorder that may cause hoarseness, dysphagia, and even aspiration, leading to considerable impairment of quality of life (1). It commonly results from dysfunction of the recurrent laryngeal nerve (RLN) innervating the intrinsic muscles of the larynx. The etiologies of UVFP include iatrogenic, neoplastic, idiopathic, neurologic, nonsurgical trauma, and other factors (2). Iatrogenic surgical injury has become the most common cause of UVFP because of the rising number of surgeries involving RLN pathway being performed. Thyroidectomy remains the leading cause of surgery-related UVFP (2, 3).

A systematic review of 27 articles and 25,000 patients revealed that the average incidence rates of temporary and permanent UVFP after thyroidectomy are 9.8% and 2.3%, respectively (4). In a large multi-institutional study, RLN injury occurred in nearly 6% of thyroid surgeries (5). The incidence of RLN palsy after thyroid surgery is up to 8% for transient palsy and ranges from 0.3% to 3% for permanent palsy (6–8).

Multiple treatment modalities have been proposed for UVFP. For example, voice therapy (VT) may be applied as a conservative and noninvasive treatment with documented clinical effectiveness (9). Injection laryngoplasty (IL), which was first introduced by Dr. Bruening in 1911, is another common treatment option for UVFP (10). Owing to advances in endoscopic technology, various injection approaches may be used in the treatment of UVFP according to the patient’s tolerance and the surgeon’s preference. Depending on the longevity of the injection materials used, IL can be performed as a temporary or long-lasting means of improving glottal insufficiency. The list of injection materials may include collagen, hyaluronic acid (HA), calcium hydroxylapatite, and other synthetic materials (11, 12). Autologous fat injection (FI) is another well-established procedure for UVFP. Lipoinjection requires overinjection by some degree to correct for the expected resorption of fat in the first 4 to 6 weeks after the procedure (13).

In contrast to IL, of which the sustainability depends on the materials used, medialization thyroplasty (MT) is considered a definite long-term treatment for UVFP. MT is performed by creating a window in the thyroid cartilage and pushing the paralyzed vocal fold medially by an implant, such as a silicone block, Gore-Tex strip, or titanium plate (14–16). Similar to IL, MT is mostly performed under local anesthesia to facilitate real-time audio feedback. It can be performed in conjunction with arytenoid adduction to further improve posterior glottal closure (17).

Although some studies have compared the surgical outcomes of patients with UVFP (18), few have focused specifically on the management and effectiveness of post-thyroidectomy UVFP. Therefore, this study investigated the voice outcomes associated with different treatment options for patients with UVFP after thyroid surgery. Our research goal was to elucidate the effectiveness of clinical treatment options for this specific clinical scenario.

Treatment for UVFP after thyroidectomy is a perennial challenge. In fact, RLN injury after thyroidectomy is a common allegation in malpractice litigations (25). According to our clinical experience, timely intervention can substantially attenuate the negative impact of UVFP after thyroidectomy and reduce patients’ willingness to file law suits. In the present study, all the treatment modalities resulted in significant voice improvement in patients with UVFP after thyroidectomy, which is consistent with the conclusions of a systematic review (18). Nevertheless, the optimal treatment strategy should be individualized according to the time interval after thyroidectomy, vocal demand, severity of complications, compliance, and expectations.

During thyroid surgery, the RLN may undergo stretch injury or accidental transection (26). In clinical practice, when vocal palsy is identified after surgery, thorough and regular follow-up every 3 to 4 weeks until the patient recovers is recommended. For patients with high vocal demand and strong motivation, VT can be applied as the first-line treatment (27). Voice training minimizes the impact of UVFP on daily life and helps patients endure the recovery period. Previous studies had documented that early referral often leads to a superior VT outcome (28). The treatment methodologies employed (e.g., the glissando maneuver to activate the cricothyroid muscles, hard glottal attacks to strengthen the adductor muscles, and resonant VT) may vary among speech pathologists. Most of these approaches are intended to enhance the laryngeal compensatory mechanisms from the healthy side. Our study results also indicated that although the degree of voice improvement associated with VT was slightly lower than that associated with the other surgical modalities, VT is still effective and well tolerated. VT remains the most common treatment for post-thyroidectomy UVFP in our routine practice ( Table 1 ).

For patients who failed to improve after VT or presented with active dysphagia shortly after thyroidectomy, IL is the most practical choice for temporary intervention. Our practice mostly uses HA in IL procedures because of its high tissue compatibility and easy access. Our previous study showed that symptomatic relief could last for 9–14 months after HA injection (22), indicating that HA is a suitable material for temporary correction of UVFP (29). Early HA injection might promote a more proper vocal fold position with improved outcomes (30), which explains why only a small fraction of the patients in the present study underwent definite MT. The greatest advantage of HA injection is that it can be performed in the clinic under local anesthesia, meaning patients do not require an additional procedure in the operating room to correct complications from the preceding thyroidectomy. HA injection can also provide rapid (sometimes immediate) voice recovery, which is beneficial for patients with high vocal demand. In addition, early HA injection can reduce the anxiety of uncertain voice recovery and ease the tension between the thyroid surgeon and the patient.

When functional recovery of phonation and swallowing is absent after 9-12 months of observation, treatment modalities with longer-lasting effects (e.g., FI and MT) are indicated. Despite the wide acceptability and tissue compatibility of autologous fat, clinical practitioners must account for the uncertain survival rates of fat grafts. Studies have reported high failure rates following FI, and patients may require revision surgery (31, 32). The variability in the clinical outcomes of the procedure can be explained by the different techniques for fat harvesting and injection. In the present study, the effects of IL with HA and fat remained similar for up to 6 months. Limited by the lack of long-term follow-up records, we are unable to determine whether fat may sustain as a long-term filler, as suggested in other studies (33).

MT is widely applied as a permanent treatment for patients with UVFP and provide satisfactory outcomes on experienced hands. However, performing an additional open surgery to correct vocal palsy caused by a previous thyroidectomy can induce substantial psychological stress for the patient. In the present study, only five of the patients agreed to undergo MT after thyroidectomy. Nevertheless, our results indicated that the voice outcomes associated with MT were superior to the other treatment modalities, especially in terms of patient-reported VHI-10 scores. A likely explanation for this trend is that MT is performed under local anesthesia, thereby enabling the patient to actively participate in the vocal tuning process.

Our study has several limitations. First, the treatment modalities were not randomized but based on shared decision between the otolaryngologist and the patient. Second, the short follow-up period limits the interpretation for long-term treatment outcomes. In addition, the treatment results of UVFP strongly depend on the surgeon’s experience, and outcomes of VT may also be influenced by the patient’s motivation and active adherence (34). Further studies with longer follow-up periods and larger samples are warranted to evaluate and compare the long-term effects of different treatment modalities for thyroidectomy-related UVFP.

UVFP is common after thyroidectomy, and common treatments include VT, HA, FI, and MT. Our results indicated significant improvements of voice outcomes associated with all these treatments. Clinical decisions may be tailored according to the surgeon’s experience, the patient’s preference and vocal demand, and the interval between thyroidectomy and intervention.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Research Ethics Review Committee of Far Eastern Memorial Hospital (FEMH No. 111032-E). Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

M-HW: Manuscript preparing and drafting, data analysis, C-TW: Study conceptualization, data analysis, manuscript drafting and proof reading. All authors contributed to the article and approved the submitted version.

This work was supported by grants from the Far Eastern Memorial Hospital (FEMH-2022-C-067 and FEMH-2022-C-068).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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