Evaluation of taste disorders
- Overview
- Theory
- Emergencies
- Diagnosis
- Resources
Summary
Taste (gustation) is attributed to sensory information received from the oral cavity and oropharynx and is the perception accompanying oral intake. Taste comprises five basic taste qualities: sweet, bitter, salty, sour, and umami. Umami (pleasant, good, desirable taste) is the perception of monosodium glutamate; its taste resembles that of chicken bouillon.[1]Chaudhari N, Landin AM, Roper SD. A metabotropic glutamate receptor variant functions as a taste receptor. Nat Neurosci. 2000;3:113-119. http://www.ncbi.nlm.nih.gov/pubmed/10649565?tool=bestpractice.com
Additional taste functions have been identified, with fat “taste” that may be mediated by receptor transduction and nonspecific transport across the cell membrane[2]Hummel T, Sekinger B, Wolf SR, et al. "Sniffin' sticks": olfactory performance assessed by the combined testing of odor identification, odor discrimination, and olfactory threshold. Chem Senses. 1997;22:39-52. http://www.ncbi.nlm.nih.gov/pubmed/9056084?tool=bestpractice.com [3]Matsuo R. Role of saliva in the maintenance of taste sensitivity. Crit Rev Oral Biol Med. 2000;11:216-229. http://cro.sagepub.com/content/11/2/216.long http://www.ncbi.nlm.nih.gov/pubmed/12002816?tool=bestpractice.com [4]Bardow A, Nyvad B, Nauntofte B. Relationships between medication intake, complaints of dry mouth, salivary flow rate and composition, and the rate of tooth demineralization in situ. Arch Oral Biol. 2001;46:413-423. http://www.ncbi.nlm.nih.gov/pubmed/11286806?tool=bestpractice.com [5]Ciancio SG. Medications' impact on oral health. J Am Dent Assoc. 2004;135:1440-1448. http://www.ncbi.nlm.nih.gov/pubmed/15551986?tool=bestpractice.com and spicy “sensation” (e.g., capsaicin, ginger) mediated by small nerve fibers. However, the common sense of the word "taste" often means "flavor," which in turn is a composite of several (nongustatory) chemosensory afferents including taste, spice, texture, and temperature (both mediated by the trigeminal nerve - i.e., cranial nerve V) and, importantly, olfaction (more precisely, retro-olfaction) perceived while eating.[6]Landis BN, Lacroix JS. Taste disorders. B-ENT. 2009;5(suppl 13):123-128. http://www.ncbi.nlm.nih.gov/pubmed/20084813?tool=bestpractice.com [7]Landis BN, Hummel T, Lacroix JS. Basic and clinical aspects of olfaction. Adv Tech Stand Neurosurg. 2005;30:69-105. http://www.ncbi.nlm.nih.gov/pubmed/16350453?tool=bestpractice.com [8]Culen M, Leopold DA. Disorders of smell and taste. Med Clin North Am. 1999;83:57-74. http://www.ncbi.nlm.nih.gov/pubmed/9927960?tool=bestpractice.com As such, a patient's complaints about taste loss do not always reflect the underlying pathology. Taste testing is mandatory to exclude a primary olfactory or trigeminal nerve pathology that manifests clinically to the patient as a problem with taste.
According to testing with taste strips, 5.3% of people considered as healthy have hypogeusia although very few have complete ageusia.[9]Welge-Lüssen A, Dörig P, Wolfensberger M, et al. A study about the frequency of taste disorders. J Neurol. 2011;258:386-392. http://www.ncbi.nlm.nih.gov/pubmed/20886348?tool=bestpractice.com The evaluation of a patient presenting with taste dysfunction comprises the patient's history (including drug intake and nutritional elements), a detailed clinical exam (including oral and dental exam), and investigations to determine the underlying etiology.[6]Landis BN, Lacroix JS. Taste disorders. B-ENT. 2009;5(suppl 13):123-128. http://www.ncbi.nlm.nih.gov/pubmed/20084813?tool=bestpractice.com [7]Landis BN, Hummel T, Lacroix JS. Basic and clinical aspects of olfaction. Adv Tech Stand Neurosurg. 2005;30:69-105. http://www.ncbi.nlm.nih.gov/pubmed/16350453?tool=bestpractice.com [8]Culen M, Leopold DA. Disorders of smell and taste. Med Clin North Am. 1999;83:57-74. http://www.ncbi.nlm.nih.gov/pubmed/9927960?tool=bestpractice.com
Applied anatomy and physiology
Taste-receptor cells are located in the taste buds, which are located on taste papillae, primarily within the oral cavity. The taste system is highly redundant, with bilateral distribution and bilateral transmission along multiple cranial nerves. There are 4 types of papillae: fungiform, foliate, circumvallate, and filiform. All, apart from filiform, have taste buds.
Afferent gustatory fibers run from the taste buds through gustatory pathways. The anterior two-thirds of the tongue is supplied by the chorda tympani, a branch of the facial nerve (cranial nerve VII). The gustatory fibers from the chorda tympani enter the brainstem via the nervus intermedius nerve (cranial nerve VII bis). At its distal end, the gustatory fibers with the chorda tympani join the lingual nerve, a part of the mandibular branch of the trigeminal nerve (cranial nerve V). Surgical procedures involving the posterior mandible may damage the lingual nerve, causing a transient or permanent loss of taste. The posterior third of the tongue is innervated by the lingual branch of the glossopharyngeal nerve (cranial nerve IX) and the base of the tongue and epiglottis by the vagus nerve (cranial nerve X). From the cranial nerves, the fibers converge in the nucleus tractus solitarius (NTS) in the brainstem. Leaving the NTS, the taste fibers still run ipsilaterally and cross partially at midbrain level, projecting in both thalami and insulae. Gustation may be altered at several levels within these pathways. Taste-receptor neurons, like olfactory-receptor neurons, are capable of regeneration.
Although it may be generally anticipated that taste complaints are related to the taste of food, some patients may report taste change in the mouth when no food is present. In some cases of taste complaint, food may taste normal and cover the abnormal taste reported when not eating. These may be reported as taste phantoms. It is important to distinguish the nature of the complaint.
Humans have at least 5 basic taste qualities that can be distinguished by taste receptors.[10]Lewis D, Dandy WE. The course of the nerve fibers transmitting sensation of taste. Arch Surg. 1930;21:249-288. Current understanding is that the entire tongue is able to perceive each of the taste qualities. Nevertheless, there are areas, such as the tip and the rear of the tongue, with higher global taste sensibilities. However, data suggest that there might be a gustotopy, similar to the cortical tonotopy related to hearing.[11]Schoenfeld MA, Neuer G, Tempelmann C, et al. Functional magnetic resonance tomography correlates of taste perception in the human primary taste cortex. Neuroscience. 2004;127:347-353. http://www.ncbi.nlm.nih.gov/pubmed/15262325?tool=bestpractice.com [12]Chen X, Gabitto M, Peng Y, et al. A gustotopic map of taste qualities in the mammalian brain. Science. 2011;333:1262-1266. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523322 http://www.ncbi.nlm.nih.gov/pubmed/21885776?tool=bestpractice.com
Saliva
Taste is an important stimulus for production of saliva and, vice versa, saliva is necessary for the perception of taste. Saliva is the natural oral solvent that dissolves food components to reach the taste receptors. Taste is also influenced by salivary composition, as a specific quality must be above normal saliva concentration in order to be perceived. Epidermal growth factor and nerve growth factor in saliva may play a role in taste function. Thus, both saliva quantity and quality can influence gustatory sensation.[4]Bardow A, Nyvad B, Nauntofte B. Relationships between medication intake, complaints of dry mouth, salivary flow rate and composition, and the rate of tooth demineralization in situ. Arch Oral Biol. 2001;46:413-423. http://www.ncbi.nlm.nih.gov/pubmed/11286806?tool=bestpractice.com Three pairs of major salivary glands and hundreds of minor glands distributed throughout the oral and pharyngeal mucosa produce saliva, which contains minerals, enzymes, and immune globulin (IgA). The system is regulated by the autonomic sympathetic and parasympathetic pathways. Physiologic, pathologic, and iatrogenic processes may interfere with salivary output and thus induce dysgeusia.
Causes of taste change
Local causes can be due to local/regional conditions, including poor oral hygiene, oral/dental/sinus disease, oral infection (e.g., candidiasis), oropharyngeal pathosis, diet, and tobacco use.
Types of taste loss
There are several ways of classifying taste disorder. The method most commonly applied in clinical practice is to distinguish qualitative from quantitative taste disturbance as follows:[13]Heckmann JG, Stössel C, Lang CJ, et al. Taste disorders in acute stroke: a prospective observational study on taste disorders in 102 stroke patients. Stroke. 2005;36:1690-1694. http://stroke.ahajournals.org/content/36/8/1690.full http://www.ncbi.nlm.nih.gov/pubmed/16002758?tool=bestpractice.com [14]Landis BN, Leuchter I, San Millan Ruiz D, et al. Transient hemiageusia in cerebrovascular lateral pontine lesions. J Neurol Neurosurg Psychiatry. 2006;77:680-683. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2117445 http://www.ncbi.nlm.nih.gov/pubmed/16614035?tool=bestpractice.com
Dysgeusia: the general terminology for any kind of taste disorder
Parageusia: qualitative taste impairment, which delineates a triggered taste distortion (e.g., bitter, metallic, or other taste perception occurs with eating/drinking)
Phantogeusia: qualitative taste impairment, which delineates a non-triggered, permanent or intermittent taste distortion, which includes several complaints, such as metallic taste or permanent bitter, sour, salty, or (even rarer) sweet taste
Hypogeusia: a quantitative taste disturbance producing reduced taste function
Ageusia: a quantitative taste disturbance producing absence of taste.
Any of these, except ageusia, can be lowered, enhanced, or unaffected by eating/drinking. These quantitative and qualitative disorders can occur together or alone (e.g., a patient with a bitter parageusia can have a normal or altered measured taste function).
Within the literature, "dysgeusia" is often used variably either as qualitative, quantitative, or general taste disorder, which can cause confusion.
Other classifications are based on the anatomic site of the lesion (e.g., peripheral nerve lesion, brainstem lesion, thalamic or fronto-orbital lesion).
Epidemiology
The epidemiology of taste disorders is unclear. Most specialized smell and taste clinics report having 10 times more olfactory disorders than pure gustatory impairments;[15]Deems DA, Doty RL, Settle RG, et al. Smell and taste disorders, a study of 750 patients from the University of Pennsylvania Smell and Taste Center. Arch Otolaryngol Head Neck Surg. 1991;117:519-528. http://www.ncbi.nlm.nih.gov/pubmed/2021470?tool=bestpractice.com however, this may reflect patterns of referral rather than true epidemiology. Olfactory impairment or loss occurs in 5% of the general population, so gustatory impairment may be present in about 0.5% of the population.[16]Landis BN, Hummel T. New evidence for high occurrence of olfactory dysfunctions within the population. Am J Med. 2006;119:91-92. http://www.ncbi.nlm.nih.gov/pubmed/16431204?tool=bestpractice.com Furthermore, taste disorders may not be noticed by the patient or the physician (e.g., in stroke) and, if testing is not performed, may be unrecognized.[13]Heckmann JG, Stössel C, Lang CJ, et al. Taste disorders in acute stroke: a prospective observational study on taste disorders in 102 stroke patients. Stroke. 2005;36:1690-1694. http://stroke.ahajournals.org/content/36/8/1690.full http://www.ncbi.nlm.nih.gov/pubmed/16002758?tool=bestpractice.com The lack of recognition and the physiologic particularities concerning taste, such as the capacity of touch to be interpreted as taste perception, suggest that taste impairments are underreported. Data suggest that around 5% of the general population have lowered taste function without necessarily being bothered by it or recognizing it.[9]Welge-Lüssen A, Dörig P, Wolfensberger M, et al. A study about the frequency of taste disorders. J Neurol. 2011;258:386-392. http://www.ncbi.nlm.nih.gov/pubmed/20886348?tool=bestpractice.com Taste change is necessarily primarily based upon patient reports, which may underestimate the epidemiology of taste changes.
Taste disorders are very common in head and neck cancer, with up to 75% of patients reporting taste loss. In some patients, full recovery does not occur and often umami taste is affected. Taste changes occur with regional radiation therapy, and with systemic chemotherapy and targeted therapies in patients having solid-tumor cancer or stem cell transplant therapy.[17]Hovan AJ, Williams PM, Stevenson-Moore P, et al. A systematic review of dysgeusia induced by cancer therapies. Support Care Cancer. 2010;18:1081-1087. http://www.ncbi.nlm.nih.gov/pubmed/20495984?tool=bestpractice.com Approximately 60% of patients receiving systemic chemotherapy will report some dysgeusia, which has been associated with the type of cytotoxic agent and the presence of oral mucositis.[18]Okada N, Hanafusa T, Abe S, et al. Evaluation of the risk factors associated with high-dose chemotherapy-induced dysgeusia in patients undergoing autologous hematopoietic stem cell transplantation: possible usefulness of cryotherapy in dysgeusia prevention. Support Care Cancer. 2016;24:3979-3985. http://www.ncbi.nlm.nih.gov/pubmed/27129837?tool=bestpractice.com Alteration of sweet and salty perception in these patients may persist up to 3 years after cessation of cancer therapy.[19]Boer CC, Correa ME, Miranda EC, et al. Taste disorders and oral evaluation in patients undergoing allogeneic hematopoietic SCT. Bone Marrow Transplant. 2010;45:705-711. http://www.ncbi.nlm.nih.gov/pubmed/19767788?tool=bestpractice.com
Differentials
Common
- Dental (periodontal) disease
- Upper respiratory tract infection
- Antimicrobial/antihypertensive therapy
- Chemotherapy/radiation therapy to the head and neck
- Dental procedure-related trauma
- Tonsillectomy
- Middle ear surgery
- Bell palsy
- Medication-related
- Burning mouth syndrome
Uncommon
- Chronic middle ear infections
- Coronavirus disease 2019 (COVID-19)
- Upper airway endoscopy
- Oral surgical procedures
- Skull base surgery
- Ramsay Hunt syndrome
- Stroke
- Head trauma
- Parkinson disease
- Alzheimer dementia
- Amyotrophic lateral sclerosis
- Multiple sclerosis
- Epilepsy
- Myasthenia gravis
- Guillain-Barre syndrome
- Sjogren syndrome
- Renal insufficiency
- Liver failure
- Diabetes mellitus
- Hypothyroidism
- Pontocerebellar angle tumors
- Paraneoplastic syndrome
- Iron deficiency
- Vitamin B12 deficiency
- Zinc deficiency
Contributors
Authors
Andrei Barasch, DMD, MDSc
Associate Professor
Weill Cornell Medical College
Division of Oncology
New York
NY
Disclosures
AB declares that he has no competing interests.
Joel Epstein, DMD, MSD, FRCD(C), FDS RCS (Edin)
Consulting Staff
Director of Oral Health Services
Division of Head and Neck Surgery
Professor of Oral Medicine
Department of Surgery
City of Hope
Duarte
Los Angeles
CA
Disclosures
JE declares that he has no competing interests.
Acknowledgements
Dr Andrei Barasch and Dr Joel Epstein would like to gratefully acknowledge Dr Stéphanie Collet, Dr Basile Nicolas Landis, and Dr Philippe Rombaux, previous contributors to this topic. SC is an author of a reference cited in this topic. BNL has been reimbursed for speaking on olfactory disorders at a neuroscience meeting in Switzerland and is an author of a number of references cited in this topic. PR is an author of a number of references cited in this topic.
Peer reviewers
Volker Gudziol, MD
ENT Specialist
Department of Otorhinolaryngology
University of Dresden Medical School
Dresden
Germany
Disclosures
VG declares that he has no competing interests.
Patient leaflets
Bell's palsy
Chronic kidney disease
More Patient leafletsLog in or subscribe to access all of BMJ Best Practice
Use of this content is subject to our disclaimer