Journal of Otology & RhinologyISSN: 2324-8785

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Research Article, J Otol Rhinol Vol: 2 Issue: 3

Post-Tonsillectomy Taste Disorders- Review of Literature

Hanna Temporale*, Krzysztof Zub, Tomasz Zatoński and Tomasz Kręcicki
Department of Otolaryngology Head and Neck Surgery, Wrocław Medical University, Poland
Corresponding author : Hanna Temporale
Borowska 213, 50-556 Wrocław, Poland
Tel: +48 606 831 562
E-mail: [email protected]
Received: May 14, 2013 Accepted: August 05, 2013 Published: August 15, 2013
Citation: Temporale H, Zub K, Zatoński T, Kręcicki T (2013) Post-Tonsillectomy Taste Disorders- Review of Literature. J Otol Rhinol 2:3. doi:10.4172/2324-8785.1000127

Abstract

Post-Tonsillectomy Taste Disorders- Review of Literature

On the basis of the available literature this review shows the characteristics, possible causes, pathophysiology and treatment of persistent taste disorders, occurring as a complication after tonsillectomy. Attention was drawn to the underestimation of the incidence of these complications and the need to inform patients assigned to tonsillectomy about the possibility of a deficit or distortion of taste after surgery.

Keywords: Tonsillectomy; Complications; Taste disorders; Dysgeusia

Keywords

Tonsillectomy; Complications; Taste disorders; Dysgeusia

Introduction

As one of the most important senses, correct perception of taste determines proper physical and mental functioning. Some claim that both taste and smell are responsible, to a large extent, for the food selection, affect human nutritional status, and their dysfunction can lead to diseases such as depression [1,2].

The Sense of Taste and its Perception

There are four basic types of taste: sweet, salty, bitter, sour and extra-fifth taste umami (the taste of glutamate). Receptors of taste - the taste buds are mainly located on the tongue, soft palate, epiglottis, upper 1/3 of esophagus, as well as on the lips, cheeks, and they are scattered in the oral mucosa [3]. The taste stimulus is transformed into a nerve impulse and it is carried from the chemoreceptors of taste buds afferently by three cranial nerves: the branch of facial nerve (VII) - special sensory fibers of chorda tympani, conducting sense of taste from the anterior 2/3 of the tongue, the glosso-pharyngeal nerve (IX) - from the base of the tongue and the vagus nerve (X) - from the soft palate, hypopharynx and epiglottis [4]. Next the impulse is transmitted to the solitary tract, then to the thalamus, neurons project to the insular cortex, the posterior limb of the internal capsule, and the operculum (primary gustatory areas).

The Role of the Glosso-Pharyngeal Nerve

The glosso-pharyngeal nerve is a mixed nerve: the bigger part consists of sensory fibers that innervate the throat (including tonsils), middle ear and tongue, the smaller part is formed by motor fibers for the throat muscles, tongue, palate and secretory (parasympathetic) to the parotid gland. Terminal branches from the nerve sensory innervate the 1/3 of the tongue.

Taste Malfunction (Dysgeusia)

An impairment or dysfunction of the sense of taste (dysgeusia) is the result of damage to the gustatory pathway that may occur at each stage. Thus epithelial, neural, and central dysgeusia can be distinguished. These disorders, depending on their nature, can be divided into quantitative (ageusia, hypogeusia, hypergeusia) and qualitative (parageusia, pseudogeusia, cacogeusia, phantogeusia). Impaired perception of all tastes is called total dysgeusia and of some selected tastes - partial dysgeusia. According to Janczewski, the most common cause of reduced sense of taste is rhinitis and other diseases with nasal blockage or coexisting smell disorders [4]. Other causes might be inflammation of the oral mucosa (e.g. after radiotherapy), systemic diseases (diabetic neuropathy, renal failure, hepatic cirrhosis), hormonal disorder (pregnancy, hypothyreoisis, adrenal insufficiency), deficiency of micronutrients (zinc, copper), avitaminosis (deficiency of vitamin A, C, and B), chronic nicotinism, alcoholism, central nervous system diseases (tumors, vascular diseases, trauma, meningitis), some mental illnesses (schizophrenia), longterm use of some medicines (e.g. captopril, metformin, imipramine, chemotherapeutics), or congenital taste buds malformation [4]. The sense of taste is impaired in the elderly. Head and neck surgeries (like ear, pharyngeal and laryngeal surgery) and tonsillectomy among them, might also affect the sense of taste.

Post-Tonsillectomy Dysgeusia

Tonsillectomy is one of the oldest and most frequently performed surgical procedures in otolaryngology. Although surgical techniques have improved over the years, complications still happen. Patients mostly suffer from pain or dysphagia. Lifethreatening complications like haemorrhage occur in 2-4% of the patients [5]. Before tonsillectomy each patient must be informed about the risk of taste impairment. Transient post-tonsillectomy taste dysgeusia (PTD) is a common complaint. Long-lasting PTD is less frequent but has significant consequences on patients’ quality of life. Transient taste perception changes seem to be relatively frequent after tonsillectomy [6-8]. They are mostly manifested by a metallic or bitter taste and generally maintain from 4 days to 2 weeks after the procedure. Persistent dysgeusia may last for 2 years or longer and retreat spontaneously [1,6,7]. The cause of this complication remains unknown, although there are several theories, which try to explain its occurrence.

Nerves Injury

Indirect and direct intrasurgical injury of the lingual or tonsillar branch of the glossopharyngeal nerve as well as pressure on the lingual nerve (along with chorda tympani nerve) caused by tongue retractor during tonsillectomy may lead to taste disturbance [1,2].
The close anatomic relationship between the palatine tonsil and the lingual branch of the glossopharyngeal nerve makes the nerve vulnerable during tonsillectomy. Clamping tonsillar branches of the lingual or facial arteries to control hemorrhage at the inferior tonsillar pole as well as using electrocautery can injure the nerve [9].
In 2004 Goins and Pitovski reported a case study of a patient with post-tonsillectomy taste disturbance. Using electrogustometry the lingual branch of the glossopharyngeal nerve (LBGN) was recognised. The patient suffered from ageusia of the posterior one-third of the tongue, which was compensated contralaterally with phantogeusia manifested by metallic or bitter taste. The report suggests that phantogeusia (taste perception despite the absence of the stimulus) might result from the release-of-inhibition in the contralateral glossopharyngeal nerve [10].
Inadvertent extension of lingual nerve and its compression during tonsillectomy may be prevented by ensuring that the tongue retractor is not fasten too tightly in the mouth, especially in cases where the mouth opening is naturally limited [1,9]. Collet et al. notes that also LBGN may be damaged in the mechanism of stretching and compression by depression of the tongue [11]. Patients, who are suspected of taste disorders caused by compression of the tongue, usually complain of hypogeusia and also of glossodynia of the tip of the tongue. In such cases, the prognosis is considered to be successful because there is no permanent damage of the nerve [12]. On the other hand, the researchers did not find that the occurrence of taste disorders after tonsillectomy was affected by the length of surgery, including the length of the use of tongue retractor [6].
Neuritis or cicatrisation during postoperative infection is considered to be another possible cause of the LBGN dysfunction [12].
Scinska et al. take into consideration the injury of the soft palate innervation: the tonsillar branch from the glossopharyngeal nerve, the palatine nerve (a branch from the maxillary nerve) or the petrosal nerve (a branch from the facial nerve) as a possible cause of dysgeusia after tonsillectomy [2]. The above observations seem to be supported by cases of taste disorders in patients with the obstructive sleep apnea syndrome (OSAS) after Uvulopaltopharyngoplasty (UPPP) [13].

The Role of Zinc in Dysgeusia

Some authors also claim that dietary zinc deficiency plays a role in the development of PTD [1,7]. It is estimated that 25% of taste and smell disorders is caused by zinc deficiency. This deficiency may lead to parakeratosis of taste buds as well as impaired function of a zinc-dependent enzyme gustin that is responsible for taste perception in the taste buds. It is assumed that, apart from low-level zinc diet, malnutrition due to postoperative pain and malabsorption, tissue injury during surgical treatment may lead to release of interleukin-1 (IL-1) and serum-tissue zinc redistribution [3]. Surgery also increases demand for zinc due to its participation in blood clotting and wound healing. Another mechanism of zinc deficiency in post tonsillectomy cases is the use of zinc-chelating medications, such as analgesics and antibiotics administered peri and postoperatively. This situation happens especially if the patient has also been undergoing long-term treatment with a zinc-chelating drug (eg. antihypertensives) before surgery [12].
Serum zinc-level test is cheap and easy to perform. However, taking into account that over 90% of zinc in the human body is located intracellularly, the results may not be indicative of the deficiency.
Zinc sulfate is used in idiopathic dysgeusia treatment. As no confirmed side effects of oral zinc supplementation have been reported such treatment is recommended in all long-lasting posttonsillectomy dysgeusia. Windfuhr et al. report a case of a female patient with a 4-year PTD who recovered within 2 months after an oral intake of zinc sulphate [7]. However, Stathas et al. did not confirm zinc, copper and ferrum disorder in serum in patients with post-tonsillectomy dysgeusia [1].

Other Investigations on Post-Tonsillectomy Dysgeusia

Drugs interactions are listed as one of taste dysfunction causes [1,12]. Some claim that pathogenesis of those disorders can be explained by the zinc chelate due to the post-operative drug treatment (pain killers, antibiotics), whilst non-chelate zinc is responsible for proper taste perception [2,12,14]. According to the literature, the use of local anesthesia and adrenaline are mentioned as one of the factors that lead to post-tonsillectomy dysgeusia [10,12,14].
A type of chosen surgical method has not been found to have any influence on the occurrence of taste impairment [1,6]. Stathas et al. compared the occurrence of taste disorders, according to two methods of tonsillectomy: the first one: using scissors and raspatory with electrocautery for coagulation, the second one: pressure-assisted tissue- welding technology, and found no statistically significant difference [1].
Other researchers studied the role of possible factors that might lead to irregulation of taste after tonsillectomy such as post-operative pain, intubation complications, operative time, hemostasis technique, wound healing. No significant correlation was observed [6]. PTD probably occurs even after uneventful tonsillectomy [6].
Several reports have pointed out the possibility of linking the occurrence of taste disorders to depression. A somatic disease and surgery increase the overall risk of depression. Dysgeusia might cause anorexia, weight loss, malnutrition, fatigue and as a result stress and depressed mood. The reports draw attention to the fact that post-tonsillectomy taste dysfunction with symptoms of depression may reflect genuine depression, not a postoperative complication. Therefore, in difficult cases, psychiatric consultation is desirable to explain the disorders [2].

Diagnostics and Evaluation of Taste Disorders

Several methods are used in the qualitative and quantitative evaluation as well as in the subjective and objective assessment of dysgeusia. Electrogustometry and specific gustometry are exerted to measure the taste perception threshold. Intensive studies conducted lately are aimed at improving the methods of evaluation of gustatory evoked potentials (GEPs) and gustatory evoked magnetic fields (GEMfs) [15,16].
Glossopharyngeal nerve damage can be diagnosed by a thermal stimulation test. It can explore the thermal and taste sensitivity of the glossopharyngeal nerve. Cruz and Green induced a bitter or sour sensation by applying a thermode to the region of the posterior third of the tongue at a temperature of 15°C for 5 to 10 seconds, whereas at 35°C there was no sensation (n=24) [17]. If the glossopharyngeal nerve is damaged, the taste and thermal sensations caused by cold disappear. The induction of a taste sensation by a thermal stimulation resulted, according to Cruz and Green [17], from the fact that the neurons sensitive to cold present in the circumvallate papillae encode according to sodium and hydrogen ion channels, which are involved in the response to an acid stimulus. In clinical practice, the sensation of cold set off by the application of cold water with a cotton-tipped applicator to the foliate papillae confirms the integrity of the glossopharyngeal nerve, and an absence or a diminution in the perception of cold is noted in the case of a lesion [18]. This test is relatively easy to carry out and is not expensive.
Dysgeusia diagnostics also involves serum zinc-level test as well as an accurate medical interview, including drug usage.

Post-Tonsillectomy Taste Disorder Treatment

Prognosis in dysgeusia after tonsillectomy is optimistic. In most cases disturbances retreat spontaneously, however, they may not retreat completely. Complete recovery of the sense of taste depends on natural healing, the regenerative capacity of the peripheral nerve fibers and gustatory pathway [10]. In transient taste malfunction it is recommended to use zinc sulfate, e.g. zinc gluconate in a dose of 140 mg daily [16]. It is essential to monitor further course of the disorders and recovery.
However some researchers underline that meticulous, saving dissection of tonsils and limited use of electrocautery may limit damage to the throat muscles and consequently reduce the risk of destruction of the surrounding structures, including branches of the nerves responsible for the reception of taste sensations [9].
Careful fixation of tongue retractor is also emphasized.

Conclusion

Post-tonsillectomy dysgeusia is still underestimated and only little attention is given to it in clinical practise. The available literature mentions nerves injury- mainly LBGN as a possible cause of taste disturbances. Other causes mentioned might be zinc deficiency and drug interactions. Typically, short-term dysgeusia does not require treatment. There are case reports with the usage of zinc sulfate as an effective therapy of persistent taste disturbances, occurring as a complication of tonsillectomy. The aim of this publication is to emphasize the problem of dysgeusia after tonsillectomy and the need of informing patients about the possible risk of dysgeusia. It is essential to take any required steps in order to prevent taste disorder and, in case it does occur, to perform the appropriate diagnostic procedures and monitor the treatment.

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