Introduction

Voice alteration and swallowing deficits are known risks of thyroid and parathyroid surgery. Post-operative change in voice has been demonstrated objectively. Acoustic analysis performed pre-operatively, and at two, four and six months post-operatively, has shown measurable changes in fundamental frequency (F₀) and shimmer values. These changes were identical in benign and malignant pathologies.^{Reference Sinagra, Montesinos, Tacchi, Moreno, Falco and Curutchet1}

Voice change is in part explained by injury to the recurrent laryngeal nerve (RLN) and superior laryngeal nerve, which run in close proximity to the thyroid gland. The RLN innervates four intrinsic muscles of the larynx. Injury leads to flaccidity of the ipsilateral vocal fold, with resultant loss of abduction and adduction. The effect varies, ranging from compensated mild dysphonia to complete paralytic aphonia. Protection of the airway becomes more difficult, causing an aspiration risk.^{Reference Crumley2}

The majority of post-operative palsies are transient.^{Reference Wagner and Seiler3} The rate of permanent unilateral RLN palsy following thyroidectomy is 1.7–5 per cent, depending on the surgical indication. Operations for malignancy and revision procedures carry a higher risk.^{Reference Lo, Kwok and Yuen4}

Routine identification of the RLN reduces the risk of permanent palsy. Hence, intra-operative nerve monitoring is now considered the standard of care.^{Reference Wagner and Seiler3} Multivariant analysis has confirmed that intra-operative nerve monitoring reduces RLN palsy rates (p < 0.001).^{Reference Abdelhamid and Aspinall5} Even with intra-operative nerve monitoring, nerve injury remains an accepted part of practice and does not represent negligence.^{Reference Rosato, Carlevato, De Toma and Avenia6}

Unilateral RLN palsy has a detrimental impact on quality of life. Palsies can be treated efficiently by safe techniques such as vocal fold injections and nerve transfer, which should be offered to all symptomatic patients.^{Reference Hartl, Travagli, Leboulleux, Baudin, Brasnu and Schlumberger7} Bilateral surgery puts both RLNs at risk; bilateral vocal fold palsy can cause a fixed larynx and threatens the airway. Rarely, emergency tracheostomy is indicated.^{Reference Friedrich, Hänsch, Eichfeld, Steinert and Schönfelder8} Whilst preservation of the RLN makes up a critical component of pre-operative consent, it is understood that voice change occurs in the absence of RLN injury.

The importance of the superior laryngeal nerve is debated. The external branch of the superior laryngeal nerve runs close to the superior thyroid vessels, and is at risk during ligation. The nerve carries motor fibres to the cricothyroid muscle, the only tensor muscle of the larynx. It was historically thought that damage was important in post-operative voice change, especially in professional voice users. This was supported by a case series which showed that voice change following hemi-thyroidectomy reduced from 11 per cent to 5 per cent if the superior laryngeal nerve was formally identified.^{Reference Kark, Kissin, Auerbach and Meikle9} However, recent data do not support this. A case series of 54 thyroidectomised patients showed that typical voice symptoms of easy fatigue and difficulties with singing voice were present even when superior laryngeal nerve palsy was excluded by electromyography testing of the cricothyroid muscle. The authors speculate that the cause of voice dysfunction is disturbance of the extralaryngeal skeleton.^{Reference Myers, Hong and Kim10} Similarly, another case series observed 47 female patients with confirmed preservation of the recurrent and superior laryngeal nerves. A mean decrease of the speaking fundamental frequency of 12 Hz was found on day 4. The range between the highest and lowest F₀ during speech was diminished, and vocal jitter elevated.^{Reference Debruyne, Ostyn, Delaere and Wellens11}

The strap muscles have been implicated in both voice change and dysphagia. The sternohyoid and sternothyroid overlie the thyroid gland, acting to depress the hyoid bone. They are routinely retracted during the surgical approach. In cases of goitre, they can be divided to improve access. However, a study analysing thyroidectomy data from two high-volume referral institutions has refuted any relationship between post-operative voice dysfunction and intra-operative division of the sternothyroid.^{Reference Henry, Solomon, Howard, Gurevich-Uvena, Horst and Coppit12} Similarly, a 44-patient case series reported that division of either strap muscle was not detrimental to voicing post-operatively.^{Reference McIvor, Flint, Gillibrand and Morton13}

At least some of the voice change can be attributed to oropharyngeal intubation. One study compared vocal performance after thyroidectomy with a breast surgery control group. Subjects underwent acoustic analysis that showed significantly increased values in the voice turbulence index in both groups. Values were higher in the those undergoing thyroid surgery.^{Reference de Pedro Netto, Fae, Vartanian, Barros, Correia and Toledo14} Even when neural and muscular damage are accounted for, there remains a cohort of patients with post-operative voice damage that is not easily explained.

Swallowing complaints following thyroid and parathyroid surgery are less well described. Again, they have been shown to cause psychological stress and reduce quality of life. Patients commonly describe a sensation of a lump, tightness, foreign body, difficulty or pain in swallowing.^{Reference Scerrino, Tudisca, Bonventre, Raspanti, Picone and Porrello15} The identification of post-operative swallowing problems is challenging as they often predate the surgery as a symptom of the thyroid disease. A recent systematic review showed a significant increase in swallowing impairment compared to baseline shortly after surgery. In the majority of patients, dysphagia reverted to pre-operative levels within two to three months of surgery. However, dysphagia persisted in a small proportion of patients at one year.^{Reference Vardaxi, Tsetsos, Koliastasi, Poutoglidis, Sapalidis and Triaridis16} Another retrospective case series showed that subjective upper aerodigestive symptoms are present in 25 per cent of patients following total thyroidectomy at a mean of four years following surgery.^{Reference Pereira, Girvent, Sancho, Parada and Sitges-Serra17}

The mechanisms underpinning post-operative dysphagia are similarly disputed. Damage to the RLN and superior laryngeal nerve again explains the cause in a subset of patients. The laryngeal protective role of the external branch of the superior laryngeal nerve has been established in porcine models.^{Reference Folk, Paskhover, Wadie, Wahba and Sasaki18} The RLN has posterior branches that provide sensory innervation to the oesophagus as inferiorly as the cricopharyngeus. Hence, palsy of either nerve causes an aspiration risk, necessitating increased awareness of the upper oesophagus. Laryngopharyngeal reflux in the post-operative period is a contributing factor. Recent data have shown that symptoms diminish in patients given proton pump inhibitors in the first week post-operatively.^{Reference Zawawi, Richardson, Varshney, Young, Mlynarek and Payne19} Other hypotheses include alteration in vascular supply, neurological damage to the sympathetic cervical chain, or damage to the extrinsic perithyroidal plexus which innervates the pharynx. The psychological response to the procedure has also been implicated. The phenomenon is likely multifactorial in origin, involving both physical and functional factors, given the variability in the symptoms experienced by patients.^{Reference Hillenbrand, Cammerer, Dankesreiter, Lemke and Henne-Bruns20,Reference Galluzzi and Garavello21}

The operative factors influencing symptom severity are better understood. The Thyroidectomy-Related Voice Questionnaire has been used to show greater symptomatology following total thyroidectomies. A concurrent neck dissection increased scores further.^{Reference Park, Oh, Cho, Baek, Kwon and Jung22} The incidence of both voice and swallowing symptoms is reduced in video-assisted surgery.^{Reference Lombardi, Raffaelli, D'Alatri, De Crea, Marchese and Paludetti23} Minimally invasive parathyroidectomy can be performed with no significant change in voice acoustic parameters.^{Reference Leder, Donovan, Acton, Warner, Carling and Alian24} A retrospective review has shown a positive correlation for voice and swallowing symptoms with age. Multivariate analysis established a 5 per cent increase in odds per year, up to the age of 50 years, after which the risk plateaued. There was no correlation with the Modified Frailty Index.^{Reference Sahli, Canner, Najjar, Schneider, Prescott and Russell25}

This study independently assessed patients’ subjective experience of dysphagia and voice change following thyroid or parathyroid surgery. Patients with operative complications including RLN injury were excluded. We focused on patients’ experience of the symptomatology to assess the holistic impact of surgery.