Ageusia: what is it, causes, treatment, complications, prognosis

What is ageusia?

Ageusia - a rare disease characterized by a complete loss of the gustatory function of the tongue. Ageusia requires discrimination from other taste disorders such as hypogeusia (decreased sensitivity to all flavoring substances), hypergeusia (increased taste sensitivity), dysgeusia (unpleasant perception of the flavoring agent) and phantogeusia (the perception of taste that occurs in the absence of flavoring agent). Although ageusia is not a life-threatening condition, it can cause discomfort. Ageusia can lead to loss of appetite, weight loss and, in some cases, may require drug withdrawal in already debilitated patients; this can lead to health problems and can have a serious psychological impact on the patient.

Causes

There are many conditions that can lead to ageusia, for example:

• damage to the gustatory nerve (lingual and lingo-pharyngeal nerves) in the anterior and posterior parts;
• malnutrition;
• system states such as hypothyroidism and diabetes, megaloblastic anemia;
• Sjogren's syndrome;
• Crohn's disease.

Cranial nerve disorders affecting gustatory function include neuritis caused by shingles, dissection of the cervical arteries, volumetric tumors in the cerebellopontine angle (meningioma or neuroma) and neoplastic processes affecting the base of the skull. Ageusia can also result from iatrogenic lesions (after laryngoscopic procedures), neuralgia and polyneuropathies (due to conditions such as diphtheria, porphyria, lupus or amyloidosis).

Patients with cancer in any area of ​​the head and neck receiving radiation therapy may have ageusia, as radiation therapy can damage taste buds, sensory neurons, and affect salivation by damaging the salivary glands, leading to dysfunction taste.

Zinc deficiency is also a cause of taste abnormalities in healthy people and cases of drug-induced taste disturbances. The disorder can also result from some local trauma and inflammation in the surrounding structure. The condition can result from burns, cuts, surgery, and local anesthesia. Taste function can also be affected by topical antiplaque medications that are secreted in saliva, some infections (dentoalveolar, periodontal and soft tissue infections), vesicular-bullous conditions, full or partial removable dentures, metal dentures and salivary dysfunction glands.

Certain drugs, including antibiotics (ampicillin, macrolides, metronidazole, quinolones, tetracycline), antineoplastic drugs, neurological drugs (antiparkinsonism, CNS stimulants, migraine drugs) cardiovascular drugs (antihypertensive drugs, diuretics, statins, antiarrhythmic drugs, antipressants), antipressants. It has also been reported that thyroid hormone preparations, antihistamines, bronchodilators, antifungals and antiviral drugs cause ageusia as a side effect.

What's more, aging or aging-related factors can also make people more vulnerable to gustatory dysfunction.

Epidemiology

Complete ageusia is very rare. Ageusia is reported to occur in 1 to 2 people out of 1000. In general, palatability deteriorates with age. However, this usually does not lead to a complete loss of gustatory sensitivity.

Pathophysiology

The sense organ specialized in taste consists of approximately 10,000 taste buds. These taste buds are ovoid bodies ranging in size from 50 to 70 micrometers. Taste receptors appear in various anatomical places, for example, in the lining of the epiglottis, palate, pharynx, and papillae of the tongue. In the apical part of each taste bud are receptors that enter the oral cavity. Within each taste bud are four morphologically distinct cell types (basal cells, type I dark cells, type I light cells, and type III intermediate cells. Basal cells are probably immature taste cells that do not spread out into taste pores. The last three types of cells are sensory neurons and are responsible for responding to gustatory stimuli or gustatory substances.

The pathophysiology of ageusia depends on the factor that caused it. Anatomical changes may occur in a person undergoing chemotherapy and radiation therapy. cells of taste buds, and sometimes death of cells of taste buds due to a higher metabolic rate cells. In addition, since saliva is important for the delivery of stimulants to taste cells, damage to the major salivary glands during cancer treatment can lead to loss of taste. The presence of infection or inflammation in nearby areas can cause apoptosis, which can lead to a decrease in the number of taste receptor cells. They can also interfere with the ability of chemosensitive hair to detect taste stimulants.

Damage to the tympanic nerve during ear surgery, laryngoscopy, or any dental surgical treatment can lead to a change in taste. The presence of any kind of infection or trauma can also damage this nerve that carries the sensory taste fibers of the tongue. Any damage to the lingual branch of the ninth cranial nerve during tonsillectomy can also lead to loss of taste. The cells of the taste buds are altered in certain systemic diseases, which can secondary to loss of taste due to neuropathy or changes in the oral environment. Violations include autoimmune diseases (Sjogren's syndrome), arterial hypertension, diabetes, renal failure, liver disease and hyperthyroidism.

The normal aging process can also lead to a deterioration in taste, but complete loss of taste is rare. Decreased taste sensation in older patients is common due to age-related regression of taste cells, decreased production of saliva and a person's inability to chew food completely correlates with the loss of teeth. In addition, geriatric patients suffer from ageusia due to polypharmacy, malnutrition and as a secondary complication of certain oral and systemic diseases.

The gustatory nucleus is a paired nucleus located in the medulla; they are also called the core of a single path. They receive impulses from the taste buds present on the tongue through the VII, IX and X cranial nerves. After receiving these impulses, the nuclei send abundant projections to various areas of the brain, such as the amygdala, bridge, lateral hypothalamus, ventral-posterior thalamic nucleus, as well as in the primary and secondary gustatory areas bark.

Histopathology

Taste receptors contain taste receptor cells of epithelial origin and stentacular cells. These cells surround a small cavity in the center that opens to the surface as a tiny gustatory pore, and both are renewed by basal cells. Chemicals present in food stimulate taste receptor cells, which convert taste stimuli into electrochemical signals. They then transmit these signals to sensory nerves.

Diagnostics

When examining patients with taste disturbances, a subjective assessment of the main complaint is necessary, as well as an objective assessment of the condition of the head, neck and oral cavity, as well as analysis of the patient's health status, dental health, taken and previously taken medications, as well as social anamnesis.

• Detailed history: to determine the etiology of the disease, events associated with the occurrence of gustatory complaints are extremely important. A complete history is also worth considering, including systemic illness, current medications, and dental procedures. Any drug change also needs to be evaluated.
• Physical examination: to identify local factors leading to the development of taste disorders, it is necessary to examine the oral cavity to identify local factors.

In addition, there are various tests for assessing taste, such as electro / chemo-gustometry and spatial analysis. Electro-gustometry is based on the principle of applying weak electric currents to various taste buds in oral cavity, while chemo-gustometry uses specific taste solutions to study the taste sensitivity. Based on these tests, the patient's ability to detect and evaluate the intensity of different types of tastes, such as sweet, salty, sour and bitter tastes, is assessed. Because localized lesions may not be found, spatial analysis evaluates different areas of the oral mucosa. In this test, a cotton swab is dipped in a tasteful solution and then applied to various areas of the oral mucosa. To assess the effectiveness of the taste buds present in the throat, the patient is asked to swallow a portion of each taste solution. The patient is then asked to rate the quality and intensity of the taste.

The clinician can also assess taste dysfunction by applying a local anesthetic (2% lidocaine unflavored) to the dorsum of the tongue. The anesthetic is applied on one side, first starting in the anterior two-thirds and gradually moving towards the posterior third, and then applied in a similar manner to the contralateral side. If the underlying complaint is resolved, the source of the taste disturbance is considered local. But if it persists, then other factors can be suspected, such as a systemic condition or some damage to the central nervous system.

In addition to the history and physical examination, psychophysical and medical imaging can also occur in the clinical assessment of a patient with a taste disorder.

• Psychophysical assessment: is necessary to identify patient complaints and measure the degree of persistent taste loss. The clinician should also be attentive to the patient's psychological state. Depression may result from taste problems or contribute to taste complaints.
• Medical imaging: it is performed to obtain anatomical and etiological diagnostic information. Imaging techniques can help rule out or confirm the presence of any damage to structures in the central nervous system, especially the brainstem, thalamus, or pons.

Treatment

For the treatment of ageusia, it is necessary to determine the etiological factor. Some taste disorders do not require treatment because they resolve spontaneously. There is no specific therapeutic regimen for a taste disorder such as ageusia. If ageusia is caused by chemotherapy, it is potentially reversible when the drugs of the disorder are discontinued. However, drug withdrawal to treat taste disorders is not always possible in patients, especially those with life-threatening conditions such as cancer, diabetes mellitus, and uncontrolled infections. Supplements such as zinc gluconate, especially in patients undergoing radiation therapy / chemotherapy at a dose of 140 mg / day, or 600 mg / day alpha lipoic acid for several months can restore taste.

In cases of dysgeusia and burning in the mouth, it is possible to use tricyclic antidepressants and clonazepam. For severe dysgeusia, local anesthetics such as lidocaine gel may help. There is no specific therapy after trauma or surgery that affects the nervous system of the taste buds. The condition may gradually improve on its own, or it may remain the same. In patients with xerostomia, artificial saliva is a treatment option.

Forecast

The success of ageusia treatment depends on the etiology. Many patients develop depressionas they remain concerned about the severity of their disorder.

Complications

Ageusia can cause serious health problems. Ageusia, if triggered by medications, can worsen various geriatric problems such as anorexia, cachexia and urinary incontinence. Ageusia may be a risk factor for cardiovascular disease, diabetes mellitus, cerebrovascular stroke and other diseases requiring a special diet.

If taste is impaired, the patient may change his eating habits and be malnourished. Some sufferers may eat less, which leads to weight loss, while others may eat more, which leads to weight gain. In severe cases, ageusia can lead to depression.