Patients presenting with taste complaints may in fact have olfactory dysfunction with abnormal flavor perception due to the loss of retronasal olfaction. With loss of flavor, a person may, for example, not perceive the strawberry flavor of ice cream but may still detect its sweetness. True taste loss includes a loss of perception of salty, bitter, sour, sweet, or savory (umami). Taste disorders can also include the perception of bad or metallic tastes. Taste perception occurs through the taste buds on the tongue, pharynx, larynx, and soft palate. All taste buds can perceive all taste qualities; the notion of a tongue “taste map” is a myth. Taste receptors are innervated by branches of the facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) cranial nerves to the nucleus of the solitary tract. Taste disorders include loss of taste (ageusia), partial loss of taste (hypogeusia), or altered taste (dysgeusia), including distortion with stimulus (parageusia) or without stimulus (phantogeusia). Taste disturbances can be due to local effects on the tongue, including local infection, injury to the papillae, mucositis, alterations in saliva, or poor oral hygiene. Injury to the chorda tympani, from trauma, ear surgery, or middle ear disease, can also affect taste. Strokes, particularly strokes involving the frontal lobe or those of the partial anterior circulation subtype, have been associated with taste disorders.79 Renal disease or diabetes may affect taste perception, as may nutritional deficiencies. Medications that can commonly affect taste include antimicrobials, anticholinergics, antidepressants, and antihypertensives such as angiotensin-converting enzyme inhibitors, although a large number of medications include altered taste as a possible side effect. Chemotherapy and radiation to the head and neck are commonly associated with taste disorders due to effects on the saliva and changes to the mucosa.
Evaluation of taste disorders includes olfactory testing as well as the assessment of perception of salty, bitter, sweet, and sour stimuli on the tongue, and a thorough head and neck exam with radiographic imaging as indicated. Treatment of taste disorders involves treatment of underlying infections, improvement of oral hygiene and saliva, changes in medication, or treatment of systemic illness. Patients with a loss of taste can be counseled to the use of flavorings or flavor enhancers and varying color, texture, and temperature of food to maximize the enjoyment of food and to avoid nutritional deficiencies.