Chapter 030. Disorders of Smell, Taste, and Hearing (Part 5)

Disorders of the Sense of Taste Disorders of the sense of taste are caused by conditions that interfere with the access of the tastant to the receptor cells in the taste bud (transport loss), injure receptor cells (sensory loss), or damage gustatory afferent nerves and central gustatory pathways (neural loss) (Table 30-2).Transport gustatory losses result from xerostomia due to many causes, including Sjögrens syndrome, radiation therapy, heavy-metal intoxication, and bacterial colonization of the taste pore.Sensory gustatory losses are caused by inflammatory and degenerative diseases in the oral cavity; a vast number of drugs, particularly those that interfere with cell...
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Chapter 030. Disorders of Smell, Taste, and Hearing (Part 5) Chapter 030. Disorders of Smell, Taste, and Hearing (Part 5) Disorders of the Sense of Taste Disorders of the sense of taste are caused by conditions that interfere withthe access of the tastant to the receptor cells in the taste bud (transport loss), injurereceptor cells (sensory loss), or damage gustatory afferent nerves and centralgustatory pathways (neural loss) (Table 30-2). Transport gustatory losses result from xerostomia due to many causes,including Sjögrens syndrome, radiation therapy, heavy-metal intoxication, andbacterial colonization of the taste pore. Sensory gustatory losses are caused by inflammatory and degenerativediseases in the oral cavity; a vast number of drugs, particularly those that interferewith cell turnover such as antithyroid and antineoplastic agents; radiation therapyto the oral cavity and pharynx; viral infections; endocrine disorders; neoplasms;and aging. Neural gustatory losses occur with neoplasms, trauma, and surgicalprocedures in which the gustatory afferents are injured. Taste buds degeneratewhen their gustatory afferents are transected but remain when their somatosensoryafferents are severed. Patients with renal disease have increased thresholds forsweet and sour tastes, which resolves with dialysis. Table 30-2 Causes of Gustatory Dysfunction Transport Gustatory Losses Neural Gustatory Losses Drugs Diabetes mellitus Heavy-metal intoxication Hypothyroidism Radiation therapy Oral neoplasms Sjögrens syndrome Oral surgery Xerostomia Radiation therapy Sensory Gustatory Losses Renal disease Aging Stroke and other CNS disorders Candidiasis Trauma Drugs (antithyroid and antineoplastic) Upper respiratory tract Endocrine disorders infections Oral neoplasms Pemphigus Radiation therapy Viral infections (especially withherpes viruses) A side effect of medication is the single most common cause of tastedysfunction in clinical practice. Xerostomia, regardless of the etiology, can beassociated with taste dysfunction. It is associated with poor oral clearance and poor dental hygiene and canadversely affect the oral mucosa, all leading to dysgeusia. However, severesalivary gland failure does not necessarily lead to taste complaints. Xerostomia, the use of antibiotics or glucocorticoids, or immunodeficiencycan lead to overgrowth of Candida; overgrowth alone, without thrush or overtsigns of infection, can be associated with bad taste or hypogeusia. When tastedysfunction occurs in a patient at risk for fungal overgrowth, a trial of nystatin orother antifungal medication is warranted. Upper respiratory infections and head trauma can lead to both smell andtaste dysfunction; taste is more likely to improve than smell. The mechanism oftaste disturbance in these situations is not well understood. Trauma to the chorda tympani branch of the facial nerve during middle earsurgery or third molar extractions is relatively common and can cause dysgeusia.Bilateral chorda tympani injuries are usually associated with hypogeusia, whereasunilateral lesions produce only limited symptoms. As noted above, aging itself may be associated with reduced tastesensitivity. The taste dysfunction may be limited to a single compound and may bemild.