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dysgeusia
Dysgeusia ( or ) or parageusia is a distortion of the sense of taste. Dysgeusia is also often associated with ageusia, which is the complete lack of taste, and hypogeusia, which is the decrease in taste sensitivity.〔Samuel K. Feske and Martin A. Samuels, ''Office Practice of Neurology'' 2nd ed. (Philadelphia: Elsevier Science, 2003) 114.〕 An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary symptom. The distortion in the sense of taste is the only symptom, and diagnosis is usually complicated since the sense of taste is tied together with other sensory systems. Common causes of dysgeusia include chemotherapy, asthma treatment with albuterol, and zinc deficiency. Different drugs could also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms of dysgeusia. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.
==Background==
The sense of taste is based on the detection of chemicals by specialized taste cells in the mouth. The mouth, throat, larynx, and esophagus all have taste buds, which are replaced every ten days. Each taste bud contains receptor cells.〔 Afferent nerves make contact with the receptor cells at the base of the taste bud.〔Brand JG. Within reach of an end to unnecessary bitterness. Lancet. 2000;356:1371-2.〕 A single taste bud is innervated by several afferent nerves, while a single efferent fiber innervates several taste buds.〔Beidler LM, Smallman RL. Renewal of cells within taste buds. J Cell Biol. 1965;27:263-272.〕 Fungiform papillae are present on the anterior portion of the tongue while circumvallate papillae and foliate papillae are found on the posterior portion of the tongue. The salivary glands are responsible for keeping the taste buds moist with saliva.〔Steven M. Bromley “Smell and taste disorders: A primary care approach,” ''American Family Physician'' 15 Jan 2000: 1.〕
A single taste bud is composed of four different types of cells, and each taste bud has at least 30 to 80 cells. Type I cells are thinly shaped, usually in the periphery of other cells. They also contain high amounts of chromatin. Type II cells have prominent nuclei and nucleoli with much less chromatin than Type I cells. Type III cells have multiple mitochondria and large vesicles. Type I, II, and III cells also contain synapses. Type IV cells are normally rooted at the posterior end of the taste bud. Every cell in the taste bud forms microvilli at the ends.〔Yasuda, M; Tomita, H (2002) “Electron microscopic observations of glossal circumvallate papillae in dysgeusic patients,” ''Acta Otolaryngol'' 126.〕
In humans, the sense of taste is conveyed via three of the twelve cranial nerves. The chorda tympani is responsible for taste sensations from the anterior two thirds of the tongue, the glossopharyngeal nerve (IX) is responsible for taste sensations from the posterior one third of the tongue while a branch of the vagus nerve (X) carries some taste sensations from the back of the oral cavity.
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