Ageusia meaning Taste Disorders

Ageusia is a symptom reflecting various underline pathological conditions. It is a rare condition that is characterized by complete loss of the taste function of the tongue. This activity describes the evaluation and management of ageusia and highlights the role of the interprofessional team in evaluating and improving care for patients with this condition.

Ageusia is a rare condition that is characterized by a complete loss of taste function of the tongue. It requires differentiation from other taste disorders such as hypogeusia (decreased sensitivity to all tastants), hypogeusia (enhanced gustatory sensitivity), dysgeusia (unpleasant perception of a tastant), and phantogeusia (perception of taste that occurs in the absence of a tastant). Although ageusia is not a life-threatening condition, it can cause discomfort. It can lead to loss of appetite, and reduction in weight, and in some cases, may require discontinuation of drugs in already compromised patients; this can result in medical problems and can have a severe psychological impact on the patient.

How common are taste disorders?

Many of us take our sense of taste for granted, but a taste disorder can have a negative effect on your health and quality of life. If you are having a problem with your sense of taste, you are not alone. More than 200,000 people visit a doctor each year for problems with their ability to taste or smell. Scientists believe that up to 15 percent of adults might have a taste or smell problem, but many don’t seek a doctor’s help.

The senses of taste and smell are very closely related. Most people who go to the doctor because they think they have lost their sense of taste are surprised to learn that they have a smell disorder instead.

How does your sense of taste work?

Your ability to taste comes from tiny molecules released when you chew, drink, or digest food; these molecules stimulate special sensory cells in the mouth and throat. These taste cells, or gustatory cells, are clustered within the taste buds of the tongue and roof of the mouth, and along the lining of the throat. Many of the small bumps on the tip of your tongue contain taste buds. At birth, you have about 10,000 taste buds, but after age 50, you may start to lose them.

When the taste cells are stimulated, they send messages through three specialized taste nerves to the brain, where specific tastes are identified. Taste cells have receptors that respond to one of at least five basic taste qualities: sweet, sour, bitter, salty, and umami [oo-MOM-ee]. Umami, or savory, is the taste you get from glutamate, which is found in chicken broth, meat extracts, and some cheeses. A common misconception is that taste cells that respond to different tastes are found in separate regions of the tongue. In humans, the different types of taste cells are scattered throughout the tongue.

Taste quality is just one way that you experience a certain food. Another chemosensory mechanism, called the common chemical sense, involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. These nerve endings give rise to sensations such as the coolness of mint and the burning or irritation of chili peppers. Other specialized nerves create the sensations of heat, cold, and texture. When you eat, the sensations from the five taste qualities, together with the sensations from the common chemical sense and the sensations of heat, cold, and texture, combine with a food’s aroma to produce a perception of flavor. It is flavor that lets you know whether you are eating a pear or an apple.

Most people who think they have a taste disorder actually have a problem with smell. When you chew food, aromas are released that activate your sense of smell by way of a special channel that connects the roof of the throat to the nose. If this channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach sensory cells in the nose that are stimulated by smells. As a result, you lose much of our enjoyment of flavor. Without smell, foods tend to taste bland and have little or no flavor.

What are taste disorders?

The most common taste disorder is phantom taste perception: a lingering, often unpleasant taste even though there is nothing in your mouth. People can also experience a reduced ability to taste sweet, sour, bitter, salty, and umami—a condition called hypogeusia [hy-po-GYOO-zee-a]. Some people can’t detect any tastes, which is called ageusia [ah-GYOO-zee-a]. True taste loss, however, is rare. Most often, people are experiencing a loss of smell instead of a loss of taste.

In other disorders of the chemical senses, an odor, a taste, or a flavor may be distorted. Dysgeusia [dis-GYOO-zee-a] is a condition in which a foul, salty, rancid, or metallic taste sensation persists in the mouth. Dysgeusia is sometimes accompanied by burning mouth syndrome, a condition in which a person experiences a painful burning sensation in the mouth. Although it can affect anyone, burning mouth syndrome is most common in middle-aged and older women.

Types of taste loss

There are several ways of classifying taste disorder. The method most commonly applied in clinical practice is to distinguish qualitative from quantitative taste disturbance as follows:[rx][rx]

• Dysgeusia: the general terminology for any kind of taste disorder

• Parageusia: qualitative taste impairment, which delineates a triggered taste distortion (e.g., bitter, metallic, or other taste perception occurs with eating/drinking)

• Phantogeusia: qualitative taste impairment, which delineates a non-triggered, permanent or intermittent taste distortion, which includes several complaints, such as metallic taste or permanent bitter, sour, salty, or (even rarer) sweet taste

• Hypogeusia: a quantitative taste disturbance producing reduced taste function

• Ageusia: a quantitative taste disturbance producing absence of taste.

Any of these, except ageusia, can be lowered, enhanced, or unaffected by eating/drinking. These quantitative and qualitative disorders can occur together or alone (e.g., a patient with a bitter parageusia can have a normal or altered measured taste function).

Within the literature, “dysgeusia” is often used variably either as qualitative, quantitative, or general taste disorder, which can cause confusion.

Other classifications are based on the anatomic site of the lesion (e.g., peripheral nerve lesion, brainstem lesion, thalamic or fronto-orbital lesion).

What causes taste disorders?

Some people are born with taste disorders, but most develop them after an injury or illness. Among the causes of taste problems are:

• Upper respiratory and middle ear infections
• Radiation therapy for cancers of the head and neck
• Exposure to certain chemicals, such as insecticides and some medications, including some common antibiotics and antihistamines
• Head injury
• Some surgeries to the ear, nose, and throat (such as middle ear surgery) or extraction of the third molar (wisdom tooth)
• Poor oral hygiene and dental problems.

Some people are born with these disorders, but most are caused by:

• Illness (for example, cold or flu, sinus infection, and allergies)
• Head injury
• Hormone changes
• Dental or mouth problems
• Nasal polyps
• Exposure to certain chemicals
• Certain medicines
• Exposure to radiation therapy for head or neck cancer
• Cocaine snorted through the nose
• Cigarette smoking

Conditions

A number of health conditions can result in dysgeusia, including:

• Dry mouth (xerostomia): There are many factors that can cause dry mouth, including some medications, Sjogren’s syndrome or radiation therapy for cancer. Without enough saliva production, your taste receptors may not be stimulated.
• Vitamin or mineral deficiencies: People who have zinc or vitamin B deficiencies are especially prone to loss of taste.
• Inflammation: Any condition that results in inflammation of the tongue can affect your taste receptors.
• Nerve damage: Some nerves are responsible for taste sensations. When these nerves are damaged, it can lead to dysgeusia. Other dysgeusia causes related to nerve damage include ear surgery, neck surgery and Bell’s palsy.
• GERD (chronic acid reflux): When stomach acid enters the mouth, it can affect your taste function. For this reason, some people with GERD develop dysgeusia.
• Neurologic disorders: Alzheimer’s disease, Parkinson’s disease and multiple sclerosis (MS) have been associated with dysgeusia.
• Metabolic disorders: Diabetes, hypothyroidism, kidney disease and other metabolic conditions can cause dysgeusia.
• Dental prosthesis: In the elderly the prosthesis can cover the soft palate and inhibit the activity of taste receptors.

Symptoms

Taste disorders include:

• Dysgeusia [dis-GYOO-zee-a], a condition in which a foul, salty, rancid, or metallic taste persists in your mouth. Dysgeusia is sometimes accompanied by Burning Mouth Syndrome, which is characterized by a painful burning sensation in your mouth.
• Hypogeusia [hy-po-GYOO-zee-a], in which your ability to taste is reduced.
• Ageusia [ah-GYOO-zee-a], in which you’re unable to taste anything.
• Foods that used to taste good now taste bad, and sometimes rotten.
• Foods that are characteristically sweet or salty no longer taste sweet or salty.
• All foods taste metallic or bitter.
• There’s a taste in your mouth even though you haven’t eaten anything.

How are taste disorders diagnosed?

Both taste and smell disorders are diagnosed by an otolaryngologist (sometimes called an ENT), a doctor of the ear, nose, throat, head, and neck. An otolaryngologist can determine the extent of your taste disorder by measuring the lowest concentration of a taste quality that you can detect or recognize. You may be asked to compare the tastes of different substances or to note how the intensity of a taste grows when a substance’s concentration is increased.

Scientists have developed taste tests in which the patient responds to different chemical concentrations. This may involve a simple “sip, spit, and rinse” test, or chemicals may be applied directly to specific areas of the tongue.

An accurate assessment of your taste loss will include, among other things, a physical examination of your ears, nose, and throat; a dental examination and assessment of oral hygiene; a review of your health history; and a taste test supervised by a health care professional.

Treatment

Diagnosis by an otolaryngologist is important to identify and treat the underlying cause of your disorder. If a certain medication is a cause, stopping or changing your medicine may help eliminate the problem. (Do not stop taking your medications unless directed by your doctor, however.) Often, the correction of a general medical problem can correct the loss of taste. For example, people who lose their sense of taste because of respiratory infections or allergies may regain it when these conditions resolve. Occasionally, a person may recover his or her sense of taste spontaneously. Proper oral hygiene is important to regaining and maintaining a well-functioning sense of taste. If your taste disorder can’t be successfully treated, counseling may help you adjust to your problem.

Determination of the etiological factor is necessary to treat ageusia. Some taste disorders do not require any treatment as they resolve spontaneously. There is no particular therapeutic regime for a taste disorder like ageusia. If it is chemotherapy-induced, it is potentially reversible by the cessation of the use of the offending medication. However,  discontinuation of drugs to treat the taste disorder is not always possible in patients, particularly with life-threatening conditions such as cancer, diabetes mellitus, and uncontrolled infections. Supplements are an option, such as zinc gluconate, particularly in patients undergoing radiotherapy/chemotherapy in the dosage of 140mg/day or alpha-lipoic acid[rx] in the dosage of 600 mg/day for a few months may restore taste.

In cases of dysgeusia and burning mouth disorder, tricyclic antidepressants and clonazepam are a possibility. With severe dysgeusia, topical anesthetics such as lidocaine gel may help. Following trauma or surgery affecting the nerve supply to the taste buds, no specific therapy is available. The condition may either improve gradually on its own or may remain the same. In patients with xerostomia, artificial saliva is a therapeutic option.

If you lose some or all of your sense of taste, here are things you can try to make your food taste better:

• Prepare foods with a variety of colors and textures.
• Use aromatic herbs and hot spices to add more flavor; however, avoid adding more sugar or salt to foods.
• If your diet permits, add small amounts of cheese, bacon bits, butter, olive oil, or toasted nuts on vegetables.
• Avoid combination dishes, such as casseroles, that can hide individual flavors and dilute taste.

Are taste disorders serious?

Taste disorders can weaken or remove an early warning system that most of us take for granted. Taste helps you detect spoiled food or liquids and, for some people, the presence of ingredients to which they are allergic.

Loss of taste can create serious health issues. A distorted sense of taste can be a risk factor for heart disease, diabetes, stroke, and other illnesses that require sticking to a specific diet. When taste is impaired, a person may change his or her eating habits. Some people may eat too little and lose weight, while others may eat too much and gain weight.

Loss of taste can cause you to add too much sugar or salt to make food taste better. This can be a problem for people with certain medical conditions, such as diabetes or high blood pressure. In severe cases, loss of taste can lead to depression.

If you are experiencing a taste disorder, talk with your doctor.

What research is being done about taste disorders?

The National Institute on Deafness and Other Communication Disorders (NIDCD) supports basic and clinical investigations of smell and taste disorders at its laboratories in Bethesda, Maryland, and at universities and chemosensory research centers across the country. These chemosensory scientists are exploring how to:

• Prevent the effects of aging on taste and smell.
• Develop new diagnostic tests.
• Understand associations between taste disorders and changes in diet and food preferences in the elderly or among people with chronic illnesses.
• Improve treatment methods and rehabilitation strategies.

Some recent chemosensory research focuses on identifying the key receptors expressed by taste cells and understanding how those receptors send signals to the brain. Researchers are also working to develop a better understanding of how sweet and bitter substances attach to their targeted receptors. This research holds promise for the development of sugar or salt substitutes that could help combat obesity or hypertension, as well as the development of bitter blockers that could make life-saving medicines more acceptable to children. Taste cells—as well as sensory cells that help you smell—are the only sensory cells in the human body that are regularly replaced throughout life. Researchers are exploring how and why this happens so that they might find ways to replace other damaged sensory cells.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions.

References

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