Table 3.
Etiology of gustatory disorders: proposed mechanisms of action.
| DISORDER | PROPOSED MECHANISM OF ACTION |
|---|---|
| Aging and Cognition130,131 | Cognitive processes like language and memory involved in taste recognition impaired in older adults |
| Increased bitterness threshold in older adults | |
| Bacterial Infections132 | Alteration of gene expression by stimulation of Toll-like receptors |
| Cancer Treatment97 | Damage to and reduced turnover of taste receptor cells |
| Loss of connectivity between receptor cells and neurons | |
| Direct neuronal damage | |
| Chronic Kidney Disease96,133,134 | Raised salivary sodium, salivary urea, salivary bicarbonate |
| Reduced salivary zinc | |
| Uremic toxins | |
| Altered axon conduction | |
| Impaired cognitive status | |
| Chronic Rhinosinusitis135,136 | Altered functionality of T2R38 bitter taste receptor |
| Chemotherapy137 | Alteration in zinc metabolism |
| Carbonic anhydrase VI deficiency | |
| Consumption of Ethyl Alcohol14,138 | Change in taste receptor sensitivity |
| Abnormalities in micronutrient absorption | |
| Changes in saliva | |
| Alterations in taste buds | |
| COVID-19 (Severe Acute Respiratory Syndrome Coronavirus 2)14,139, 140, 141, 142, 143, 144 | Damage to the central nervous system by the virus attaching to the angiotensin-converting enzyme 2 receptors in glial cells and spinal neurons |
| Abnormal zinc homeostasis | |
| Increased proinflammatory cytokines | |
| Direct infection of cells in the tongue | |
| Consequences of obstruction of taste cells chemesthesis due to inflammation and damage to cranial nerves VII, IX, and X | |
| Diabetes Mellitus145, 146, 147 | Xerostomia secondary to diabetes mellitus |
| Diabetic neuropathy | |
| Reduction in innervation of taste buds | |
| Increased apoptosis of taste buds | |
| Lower density of the fungiform papillae | |
| Drug Induced14,99,148, 149, 150 | Hyposalivation |
| Adverse effects on taste receptors | |
| Adverse effects on taste neural pathway | |
| Abnormalities in neurotransmitter function | |
| Fungal Infection, Candida albicans99,151 | Mechanical barrier by formation of pseudomembrane due to disproportional overgrowth |
| Genetic Disorders14,152, 153, 154 | Reduced number of taste papillae |
| Changes in taste phenotypes | |
| HIV and AIDS99,155,156 | Directly affects gustatory neurons |
| Development of local lesions | |
| Xerostomia | |
| Chemosensory alterations secondary to antiretroviral therapy | |
| Neuronal degeneration secondary to HIV leukoencephalopathy | |
| Liver Failure99 | Deficiency of vitamins B and C, zinc, and copper |
| Multiple Sclerosis99,157 | Central demyelination |
| Neurodegenerative Disorders (Dementia, Alzheimer, and Others)147,158,159 | Insular atrophy |
| Secondary to effect of medications used for management | |
| Amyloid deposition in the insula and amygdala | |
| ParkinsonDisease147,160, 161, 162 | Neurodegenerative changes of the frontal operculum or orbitofrontal cortex |
| Other concomitant factors: depression, poor oral hygiene, gastrointestinal disease, and zinc deficiency | |
| Rheumatoid Arthritis163 | Neuropathy of terminal nerve fibers |
| Neuropathy secondary to rheumatoid arthritis drugs | |
| SjögrenSyndrome99 | Excessive dryness of the oral cavity and hyperviscosity of saliva |
| Stroke99,164 | Injury to the insula, pons, thalamus, midbrain, and internal capsule |
| Systemic Lupus Erythematosus165,166 | Proinflammatory cytokines |
| Inhibition of turnover of taste bud cells by inflammation | |
| Thyroid Disorder167,168 | Zinc deficiency secondary to thyroid disease |
| Reduced cognitive functions | |
| Toxins: Environmental169,170 | Chemosensory dysfunction |
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| Affecting blood flow to tongue | |
| Direct interaction with saliva | |
| Heavy metals concentration in saliva producing harmful changes in taste receptors | |
| Viral Diseases14,132 | Nasal blockage; increased mucus production |
| Changes in olfaction | |
| Inflammation affecting gene expression in taste bud cells |