Chemosensory Function and Dysfunction

Abstract

Taste and smell are fundamental sensory systems essential in nutrition and food selection, for the hedonic and sensory experience of food, for efficient metabolism, and, in general, for the maintenance of a good quality of life. The gustatory and olfactory systems demonstrate a diversity of transduction mechanisms, and during the last decade, considerable progress has been made toward our understanding of the basic mechanisms of taste and smell. Understanding normal chemosensory function helps clarify the molecular events that underlie taste and smell disorders. At least 2,000,000 Americans suffer from chemosensory disorders-a number that is likely to grow as the aging segment of the population increases. Smell disorders are more frequent than taste disturbances, due to the vulnerability and anatomical distinctiveness of the olfactory system, and because a decline in olfactory function is part of the normal aging process. Common gustatory and olfactory complaints are due to a number of medications, to upper respiratory infections, to nasal and paranasal sinus diseases, and to damage to peripheral nerves supplying taste and smell. Most chemosensory complaints have an identifiable cause. Although diagnosis of taste and smell disorders has improved considerably over the last two decades, treatment of these disorders is still limited to conditions with discernible and reversible causes. Future research is needed for a better understanding of chemosensory mechanisms, establishing improved diagnostic procedures, and disseminating knowledge on chemosensory disorders among practitioners and the general public.

Oral Sequelae of Head and Neck Radiotherapy

“…The loss of taste is not only a result of the effect of irradiation on the taste buds, but is also related to the reduction in salivary flow rate. A reduced salivary flow decreases transport and solubilization of gustatory stimulants, reduces the ability of saliva to protect the mucosa against bacteria, fungi, and variation in the oral pH, alters the ionic composition of saliva which is important for taste, and affects mastication, nutrition, and the hedonic aspects of tasting (Spielman, 1998). Direct radiation damage to the taste buds or their innervating nerve fibers has been reported as the main cause of taste loss (Conger, 1973;Dreizen et al, 1977b;Mossman, 1986).…”

“…The degree of taste recovery and the recovery time depend on the radiation dose received. Some patients may retain a residual reduction in taste acuity (hypogeusia), or even a permanent impairment in sensation (dysgeusia) (Conger, 1973;Dreizen et al, 1977b;Mossman et al, 1982;Toljanic and Saunders, 1984), but near-normal suprathreshold levels of taste in irradiated patients have been reported as well (Schwartz et al, 1993;Spielman, 1998). These obvious discrepancies between measurable taste loss and subjective awareness of taste loss may be due to adaptation of the patient to the sensory loss (Mossman et al, 1982).…”

“…Also, further studies are needed to evaluate the effect of irradiation on von Ebner's glands and the residual flow from these glands. This may be sufficient to obscure the interpretation of currently available data (Spielman, 1998). If so, radiotherapy treatment plans should attempt to spare these glands if possible.…”

Oral Adverse Drug Reactions to Cardiovascular Drugs

“…One possibility is that the excretion of the drug or its metabolites into saliva may generate an unpleasant taste. Many chemosensory disorders affect both taste and smell, and often patients refer to a taste deficit that is actually anosmia, e.g., inability to detect olfactory stimulants (Spielman, 1998). In scalded mouth syndrome, sometimes included as an ODR, taste perception is normal; however, patients complain of a burning sensation comparable with having been scalded by a hot liquid (Vlasses et al, 1982).…”

Olfactory Dysfunction in Neurodegenerative Diseases

“…Olfactory dysfunction can lead to changes of dietary habits that may in turn exacerbate disease states or contribute to nutritional deficiencies (72,73). Although diagnosis of taste and smell disorders has improved considerably over the last two decades, treatment of these disorders is still limited to conditions with discernible and reversible causes (71,72).…”