Healthy individuals normally have a diverse range of microbial organisms residing in their oral cavities; however, chemotherapy can permit these typically non-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. Saliva is an important component of the taste mechanism. Saliva both interacts with and protects the taste receptors in the mouth. Saliva mediates sour and sweet tastes through bicarbonate ions and glutamate, respectively. The salt taste is induced when sodium chloride levels surpass the concentration in the saliva. It has been reported that 50% of chemotherapy patients have had either dysgeusia or another form of taste impairment. Examples of chemotherapy treatments that can lead to dysgeusia are cyclophosphamide, cisplatin, vismodegib, and etoposide. The exact mechanism of chemotherapy-induced dysgeusia is unknown. Taste buds
Distortions in the taste buds may give rise to dysgeusia. In a study conducted by Masahide Yasuda and Hitoshi Tomita from Nihon University of Japan, it has been observed that patients with this taste disorder have fewer 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. Zinc deficiency
Another primary cause of dysgeusia is zinc deficiency.
Because taste disorders can have detrimental effects on a patients quality of life, more research needs to be conducted concerning possible treatments such as zinc supplementation. Altering drug therapy
The effects of drug-related dysgeusia can often be reversed by stopping the patients regimen of the taste altering medication. In one case, a forty-eight-year-old woman who had hypertension was being treated with valsartan. Due to this drugs inability to treat her condition, she began taking a regimen of eprosartan, an angiotensin II receptor antagonist. Within three weeks, she began experiencing a metallic taste and a burning sensation in her mouth that ceased when she stopped taking the medication. When she began taking eprosartan on a second occasion, her dysgeusia returned. In a second case, a fifty-nine-year-old man was prescribed amlodipine in order to treat his hypertension. After eight years of taking the drug, he developed a loss of taste sensation and numbness in his tongue. When he ran out of his medication, he decided not to obtain a refill and stopped taking amlodipine. Following this self-removal, he reported experiencing a return of his taste sensation. Once he refilled his prescription and began taking amlodipine a second time, his taste disturbance reoccurred. 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. It appears that drug-induced dysgeusia can be alleviated by reducing the drugs dose or by substituting a second drug from the same class.