Dysgeusia

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Dysgeusia
Other namesParageusia
Pronunciation
SpecialtyNeurology

Dysgeusia, also known as parageusia, is a distortion of the sense of taste. Dysgeusia is also often associated with

albuterol, and zinc deficiency. Liver disease, hypothyroidism, and rarely, certain types of seizures
can also lead to dysgeusia. Different drugs can also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.

Signs and symptoms

The alterations in the sense of

smell are the only symptoms.[2]

Causes

Chemotherapy

A major cause of dysgeusia is

pathogenic agents to cause serious infection, which may result in a decrease in saliva. In addition, patients who undergo radiation therapy also lose salivary tissues.[4] Saliva is an important component of the taste mechanism. Saliva both interacts with and protects the taste receptors in the mouth.[5] Saliva mediates sour and sweet tastes through bicarbonate ions and glutamate, respectively.[6] The salt taste is induced when sodium chloride levels surpass the concentration in the saliva.[6] It has been reported that 50% of chemotherapy patients have had either dysgeusia or another form of taste impairment.[3] Examples of chemotherapy treatments that can lead to dysgeusia are cyclophosphamide, cisplatin, vismodegib,[7] and etoposide.[3] The exact mechanism of chemotherapy-induced dysgeusia is unknown.[3]

Taste buds

Distortions in the

microvilli than normal. In addition, the nucleus and cytoplasm of the taste bud cells have been reduced. Based on their findings, dysgeusia results from loss of microvilli and the reduction of Type III intracellular vesicles, all of which could potentially interfere with the gustatory pathway. Radiation to head and neck also results in direct destruction of taste buds, apart from effects of altered salivary output.[8]

Zinc deficiency

Another primary cause of dysgeusia is zinc deficiency. While the exact role of zinc in dysgeusia is unknown, it has been cited that zinc is partly responsible for the repair and production of taste buds. Zinc somehow directly or indirectly interacts with carbonic anhydrase VI, influencing the concentration of gustin, which is linked to the production of taste buds.[9] It has also been reported that patients treated with zinc experience an elevation in calcium concentration in the saliva.[9] In order to work properly, taste buds rely on calcium receptors.[10] Zinc "is an important cofactor for alkaline phosphatase, the most abundant enzyme in taste bud membranes; it is also a component of a parotid salivary protein important to the development and maintenance of normal taste buds".[10]

Taste Modifiers

Miraculin Found in miracle berries, sweetens nonsweet food and beverages.

Gymnema sylvestre Blocks the ability to taste sweetness.

Drugs

There are also a wide variety of drugs that can trigger dysgeusia, including

Wall Street Journal.[14]

The

sulfhydryl groups, including penicillamine and captopril, may react with zinc and cause deficiency.[10] Metronidazole and chlorhexidine have been found to interact with metal ions that associate with the cell membrane.[15] Drugs that act by blocking the renin–angiotensin–aldosterone system, for example by antagonizing the angiotensin II receptor (as eprosartan does), have been linked to dysgeusia.[16] There are few case reports claiming calcium channel blockers like Amlodipine also cause dysgeusia by blocking calcium sensitive taste buds.[17]

Pregnancy

Changes in hormone levels during pregnancy, such as estrogen, can affect the sense of taste.[18] A study found that 93 percent of pregnant women reported some change in taste during pregnancy.[18]

Miscellaneous causes

Xerostomia, also known as dry mouth syndrome, can precipitate dysgeusia because normal salivary flow and concentration are necessary for taste. Injury to the glossopharyngeal nerve can result in dysgeusia. In addition, damage done to the pons, thalamus, and midbrain, all of which compose the gustatory pathway, can be potential factors.[19] In a case study, 22% of patients who were experiencing a bladder obstruction were also experiencing dysgeusia. Dysgeusia was eliminated in 100% of these patients once the obstruction was removed.[19] Although it is uncertain what the relationship between bladder relief and dysgeusia entails, it has been observed that the areas responsible for urinary system and taste in the pons and cerebral cortex in the brain are close in proximity.[19]

Dysgeusia can be a symptom of head and neck cancer. In this case it often present together with having dry mouth.[20]

Dysgeusia often occurs for unknown reasons. A wide range of miscellaneous factors may contribute to this taste disorder, such as

menopausal women, often have dysgeusia as well.[22]

Normal function

The sense of taste is based on the detection of chemicals by specialized taste cells in the mouth. The mouth, throat, larynx, and esophagus all have

salivary glands are responsible for keeping the taste buds moist with saliva.[25]

A single taste bud is composed of four types of cells, and each taste bud has between 30 and 80 cells. Type I cells are thinly shaped, usually in the periphery of other cells. They also contain high amounts of

microvilli at the ends.[8]

Diagnosis

In general,

olfactory disorders.[27]

Diagnosis of dysgeusia begins with the patient being questioned about

diabetes mellitus, hypothyroidism, or cancer.[28] A clinical examination is conducted and includes an inspection of the tongue and the oral cavity. Furthermore, the ear canal is inspected, as lesions of the chorda tympani have a predilection for this site.[28]

Gustatory testing

In order to further classify the extent of dysgeusia and clinically measure the sense of taste, gustatory testing may be performed. Gustatory testing is performed either as a whole-mouth procedure or as a regional test. In both techniques, natural or electrical stimuli can be used. In regional testing, 20 to 50 μL of liquid stimulus is presented to the

posterior tongue using a pipette, soaked filter-paper disks, or cotton swabs.[27] In whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient is asked to swish the solution around in the mouth.[27]

Threshold tests for sucrose (sweet), citric acid (sour), sodium chloride (salty), and quinine or caffeine (bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test".[29] In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water.[29] Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row.[29]

Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour).

sensory system, such as the loudness of a tone, on a similar scale.[30] For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones.[30]

Other tests include identification or discrimination of common taste substances.

Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily.[27] In addition to techniques based on the administration of chemicals to the tongue, electrogustometry is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical direct current. Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue.[31] Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.[32]

Diagnostic tools

Certain diagnostic tools can also be used to help determine the extent of dysgeusia.

blink reflex may be used to evaluate the integrity of the trigeminal nerve–pontine brainstem–facial nerve pathway, which may play a role in gustatory function.[33]

Structural imaging is routinely used to investigate

cardiovascular factors appears to be useful in the diagnosis of autonomic nervous system disorders in burning mouth syndrome and in patients with inborn disorders, both of which are associated with gustatory dysfunction.[35] Cell cultures may also be used.[36]

In addition, the analysis of

pathological changes in the taste buds of patients with dysgeusia and other gustatory disorders.[38]

Treatments

Artificial saliva and pilocarpine

Main article: Artificial saliva

Because medications have been linked to approximately 22% to 28% of all cases of dysgeusia, researching a treatment for this particular cause has been important.

taste buds.[39]

Zinc deficiency

Zinc supplementation

Zinc Gluconate.
Zinc Gluconate.

Approximately one half of drug-related taste distortions are caused by a

blood serum.[42] There is not a sufficient amount of evidence to determine whether or not zinc supplementation is able to treat dysgeusia when low zinc concentrations are not detected in the blood.[42]

A Cochrane Review in 2017 assessed the effects of different interventions for the management of taste disturbances. There was very low-quality evidence to support the role of zinc supplementation in the improvement of taste acuity and taste discrimination in patients with zinc deficiency or idiopathic taste disorders. Further research is required to improve the quality of evidence for zinc supplementation as an effective intervention for the management of dysgeusia.[43]

Zinc infusion in chemotherapy

It has been reported that approximately 68% of cancer patients undergoing

immunocompromised cancer patients.[44] Because taste disorders can have detrimental effects on a patient's quality of life, more research needs to be conducted concerning possible treatments such as zinc supplementation.[46]

Altering drug therapy

Eprosartan.
Eprosartan.

The effects of drug-related dysgeusia can often be reversed by stopping the patient's regimen of the taste altering medication.

angiotensin II receptor antagonist.[48] Within three weeks, she began experiencing a metallic taste and a burning sensation in her mouth that ceased when she stopped taking the medication.[48] When she began taking eprosartan on a second occasion, her dysgeusia returned.[48] In a second case, a fifty-nine-year-old man was prescribed amlodipine in order to treat his hypertension.[49] After eight years of taking the drug, he developed a loss of taste sensation and numbness in his tongue.[49] When he ran out of his medication, he decided not to obtain a refill and stopped taking amlodipine.[49] Following this self-removal, he reported experiencing a return of his taste sensation.[49] Once he refilled his prescription and began taking amlodipine a second time, his taste disturbance reoccurred.[49] These two cases suggest that there is an association between these drugs and taste disorders. This link is supported by the "de-challenge" and "re-challenge" that took place in both instances.[49] It appears that drug-induced dysgeusia can be alleviated by reducing the drug's dose or by substituting a second drug from the same class.[39]

Alpha lipoic acid

Alpha Lipoic Acid

neuropathy.[51] ALA has proven to be an effective treatment for burning mouth syndrome, spurring studies in its potential to treat dysgeusia.[51] In a study of forty-four patients diagnosed with the disorder, one half was treated with the drug for two months, while the other half, the control group, was given a placebo for two months, followed by a two-month treatment of ALA.[51] The results showed that 91% of the group initially treated with ALA reported an improvement in their condition compared to only 36% of the control group.[51] After the control group was treated with ALA, 72% reported an improvement.[51] This study suggests that ALA may be a potential treatment for patients, and supports that full double blind randomized studies should be performed.[51]

Managing dysgeusia

In addition to the aforementioned treatments, there are also many management approaches that can alleviate the symptoms of dysgeusia. These include using non-metallic silverware, avoiding metallic- or bitter-tasting foods, increasing the consumption of foods high in protein, flavoring foods with spices and seasonings, serving foods cold in order to reduce any unpleasant taste or odor, frequently brushing one's teeth and utilizing mouthwash, or using sialogogues such as sugar-free gum or sour-tasting drops that stimulate the production of saliva.[44] When taste is impeded, the food experience can also be improved through means other than taste, such as texture, aroma, temperature, and color.[47]

Psychological impacts

People with dysgeusia are also forced to manage the impact that the disorder has on their quality of life. An altered sense of taste has effects on food choice and intake, and can lead to weight loss, malnutrition, impaired immunity, and a decline in health.[47] Patients diagnosed with dysgeusia must use caution when adding sugar and salt to food, and must be sure not to overcompensate for their lack of taste with excess amounts.[47] Since the elderly are often on multiple medications, they are at risk for taste disturbances, increasing the chances of developing depression, loss of appetite, and extreme weight loss.[52] This is cause for evaluation and management of their dysgeusia. In patients undergoing chemotherapy, taste distortions can often be severe, and make compliance with cancer treatment difficult.[45] Other problems that may arise include anorexia, and behavioral changes that can be misinterpreted as psychiatric delusions regarding food.[53] Symptoms including paranoia, amnesia, cerebellar malfunction, and lethargy can also manifest when undergoing histidine treatment.[53]

Future research

Every year, more than 200,000 individuals see their physicians concerning

University of Connecticut Health Center is integrating behavioral, neurophysiological, and genetic studies involving stimulus concentrations and intensities, in order to better understand taste function.[55]

See also

References

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