Ageusia is the loss of taste functions in the tongue. These functions include but are not limited to detecting sweetness, sourness, bitterness, and saltiness. The tongue can only detect texture and differentiate between those functions. Because of this, most of our sense of taste actually comes from the sense of smell. Ageusia is diagnosed by an otolaryngologist (ear, nose, and throat specialist) by measuring the lowest concentration of taste quality one can detect or recognize.
The loss of taste can be a side effect or a primary sign or symptom of a disease process. Thus, ageusia is caused by a number of issues including but not limited to (1) neurological damage, (2) endocrine system problems, (3) cancers of the mouth and tongue, (4) side effects of medications in cardiac and extracardiac vascular diseases, or (5) other causes. Bell’s palsy, familial dysautonomia, and multiple sclerosis are diseases that are commonly associated with neurological damage to the cranial nerves that supply the tongue and provide the sensation of taste, thus causing ageusia. These nerves are the glossopharyngeal—or cranial nerve IX—and chorda tympani nerve, which is a branch of the facial nerve—or cranial nerve VII. Specifically, the chordatympani nerve passes through and innervates the front two-thirds of the tongue while the glossopharyngeal nerve passes through and innervates the back third of the tongue.
Disorders of the endocrine system such as Cushing’s syndrome, hypothyroidism, and diabetes mellitus have also been known to cause ageusia. These are generally due to an imbalance of hormones, either over- or underexposure. These hormone levels are necessary to maintain homeostasis of the body. In Cushing’s syndrome, there is a prolonged exposure to cortisol, which can also lead to issues including but not limited to high blood pressure, abnormal obesity, and weak muscles. Conversely, hypothyroidism is when a person’s thyroid is underactive, resulting in a decreased production of thyroid hormone by the thyroid gland. Hypothyroidism can lead to a person having increased weight gain, fatigue, dry skin and hair, and a poor ability to tolerate cold. Multiple sclerosis is a demyelinating disease in which the myelin—insulation and covering of nerve cell axons—in the brain and spinal cord are damaged, resulting in slower and/or lost transmission of nerve signals. When damaged, parts of the nervous system cannot communicate with each other, causing symptoms such as loss of sensitivity, muscle weakness, and feeling tired. Other causes of ageusia include but are not limited to tobacco use, denture use, cancer, and renal failure.
The treatment of ageusia is solely dependent on the source of the disease. If it is due to tobacco use, then a primary care provider can help a person work on quitting or reducing nicotine intake. If it is due to an endocrine or a neurological problem, then common treatments are changing a person’s medication(s), diet, and/or lifestyle. Sometimes surgery may be effective in treating ageusia, but it should be an option only when all other treatments have been thoroughly tried. If ageusia is caused purely by a person’s older age, then no known medical treatments are available. It is a permanent disorder and all that can be done is to learn how to cope with the reduced or loss of taste. Health care providers can help a patient learn how to prepare foods that have more color and spices in order to stimulate any remaining taste ability along with visual stimulation of the food. This has been shown to help individuals with ageusia still obtain healthy nutrition through eating food.
See also: Dysgeusia; Familial Dysautonomia; Taste Bud; Taste System
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