Dysgeusia

Definition

Dysgeusia is a disorder of the sense of taste.

Description

Any condition that affects the ability to taste is referred to as dysgeusia. While dysgeusia is often used to describe any change in the sense of taste, more specific terms include ageusia (complete loss of the sensation of taste); hypogeusia (decreased sense of taste); parageusia (bad taste in the mouth); and dysgeusia (distorted sense of taste, such as a metallic taste in the mouth). A wide variety of conditions can cause a deficit in the sense of taste, including any conditions that interfere with the functioning of the taste buds (the nerve cells on the tongue that process information about taste), conditions that interrupt the taste signal that is sent to the brain, or conditions that interfere with the normal brain processing of those signals. Processes that affect the functioning of the lingual nerve or the glossopharyngeal nerve may impair the sense of taste. Furthermore, the sense of taste is frequently dulled or impaired due to dysfunction of the sense of smell.

Causes and symptoms

There are a wide variety of conditions that can cause dysgeusia, including:

• smoking
• respiratory infections (colds, sinus infections, throat infection, or pharyngitis)
• strep throat
• inflammation of the tongue (glossitis)
• gingivitis
• influenza
• dry mouth (due to medications or disorders such as Sjogren's syndrome or salivary gland disorders or infections)
• vitamin deficiencies (such as B-12 and zinc)
• Cushing's disorder
• cancer
• diabetes
• hypothyroidism
• liver or kidney failure
• head injuries
• brain tumors or other tumors that destroy or injure areas of the nose, mouth, throat, or brain responsible for taste
• nasal polyps
• Bell's palsy
• multiple sclerosis

In addition, normal aging usually includes a decrement in the sense of taste as the numbers of taste buds decrease over time. A large number of medications can affect the sense of taste; antibiotics and cancer chemotherapeutic agents are common culprits. Examples of drugs that are known to cause dysgeusia include lithium, penicillamine, procarbazine, rifampin, vinblastine, vincristine, captopril, griseofulvin, and thyroid medications. Radiation therapy may cause dysgeusia.

Symptoms of dysgeusia include decreased acuity of the sense of taste or the distorted perception of an odd taste. Complete loss of taste sensation is relatively rare.

Diagnosis

Diagnosis can be made by having an individual taste and smell a variety of test substances. CT or MRI imaging may reveal the disorder underlying the development of dysgeusia.

Treatment team

Dysgeusia may be treated by a neurologist or by the physician who is treating the underlying condition responsible for the disorder (such as an otorhinolaryngologist for various ear, nose, or throat conditions, such as nasal polyps).

Treatment

Some types of dysgeusia resolve on their own, particularly dysgeusia that occurs due to an infection. When the infection clears, the dysgeusia usually abates and the sense of taste returns. When smokers stop smoking, their sense of taste may improve over time. Stopping some medications may also lead to an improved sense of taste. Individuals who suffer from dry mouth (xerostomia) may benefit from artificial saliva. Individuals with nasal polyps may note improved sense of taste after polyp removal.

Prognosis

Dysgeusia secondary to infection or reversible conditions like Bell's palsy may improve partially or completely with resolution of the infection or condition; dysgeusia due to medication use or smoking may also improve partially or completely when the individual stops using the medication or discontinues smoking. However, dysgeusia due to more permanent damage to the neurological apparatus responsible for taste or smell (such as head injury, multiple sclerosis, radiation treatments, or diabetes) may never improve.

Special concerns

Individuals with severely compromised taste or smell may inadvertently eat spoiled foods, leading to food-borne illness. Furthermore, without a good sense of smell or taste, there is an increased risk that an individual will not be able to protect him- or herself from exposure to other toxins, pollution, or smoke. Individuals with an impaired sense of taste may over-salt or over-sugar their food, in an attempt to compensate. They may not take in a reasonably balanced, nutritious diet with sufficient calories, because eating may become unenjoyable.

BOOKS

Pryse-Phillips, William, T. Jock Murray, and James Boyd. "Toxic Damage to the nervous system." In Noble: Textbook of Primary Care Medicine, edited by John Noble, et al. St. Louis: W. B. Saunders Company, 2001.

PERIODICALS

Bromley, Steven M. "Smell and Taste Disorders: A Primary Care Approach." American Family Physician (January 2000).

Ritchie, C. S. "Oral health, taste, and olfaction." Clin Geriatr Med 18, no. 4 (November 2002): 709–717

Rosalyn Carson-DeWitt, MD