Ageusia

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(Redirected from Taste blindness)
Ageusia
Pronunciation
SpecialtyNeurology

Ageusia (from negative prefix a- and Ancient Greek γεῦσις geûsis 'taste') is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning 'savory taste'). It is sometimes confused with anosmia – a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.[1][2]

Even though ageusia is considered relatively rare it can impact individuals of any age or demographic. Due to the COVID-19 pandemic, there has been an increase in reported cases of ageusia, making it more commonly diagnosed than before.[3]

Causes[edit]

Ageusia can stem from various underlying causes, including, sinusitis, the common cold, influenza, head traumas, infections of upper respiratory tract, exposure to toxic substances, iatrogenic causes, medicines, glossodynia (burning mouth syndrome (BMS))[2] and COVID-19.[4]. Additionally, bacterial infections such as strep throat and salivary gland infections may also lead to this condition. [3]

Lifestyle factors like smoking, obesity, and poor nutrition contribute to ageusia, as can systemic conditions like diabetes and high blood pressure. Nutritional deficiencies, particularly in zinc and vitamin B-12 can further heighten the risk of ageusia.[3]

Neurological damage[edit]

Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the chorda tympani nerve and the glossopharyngeal nerve. The chorda tympani nerve passes taste for the front two-thirds of the tongue and the glossopharyngeal nerve passes taste for the back third of the tongue. The lingual nerve (which is a branch of the trigeminal V3 nerve, but carries taste sensation back to the chorda tympani nerve to the geniculate ganglion of the facial nerve) can also be damaged during otologic surgery, causing a feeling of metal taste.[citation needed]

Problems with the endocrine system[edit]

Deficiency of vitamin B3 (niacin) and zinc can cause problems with the endocrine system, which may cause taste loss or alteration. Disorders of the endocrine system, such as Cushing's syndrome, hypothyroidism and diabetes mellitus, can cause similar problems. Ageusia can also be caused by medicinal side-effects from antirheumatic drugs such as penicillamine, antiproliferative drugs such as cisplatin, ACE inhibitors, and other drugs including azelastine, clarithromycin, terbinafine, and zopiclone.[citation needed]

COVID-19[edit]

Main article: Symptoms of COVID-19 § Loss of taste and chemesthesis

Agnosia and anosmia in COVID-19 patients occur independently of nasal obstruction or other rhinitis symptoms, likely attributed to direct viral damage to olfactory and gustatory receptors[5]

Olfactory dysfunction has become a prominent symptom associated with a COVID-19 infection, as supported by growing evidence. Taste dysfunction has often been linked more closely with retronasal olfactory dysfunction rather than a direct impairment of taste itself. Research suggests that taste dysfunction may also present independently, rather than solely as part of an olfactory dysfunction trajectory. This unique tendency of SARS-CoV-2 to induce selective neurological impairment could contribute to the diverse presentation of taste and olfactory dysfunction observed.[6]

Research exploring the prevalence of taste disorders resulting from the COVID-19 pandemic suggests that a diverse range of individuals were affected. In European patients, the prevalence was reported at 55.2%, while in North American patients, it was 61.0%. Among Asian patients, the prevalence was lower at 27.1%, and similarly, in South American patients, it was 29.5%. Australian patients exhibited a prevalence of 25.0%. Furthermore, specific types of taste disorders were also noted, with ageusia observed in 28.0% of patients, hypogeusia in 33.5%, and dysgeusia in 41.3%.[6]

Comparisons among the different taste disorders show that dysgeusia, characterized by altered or distorted taste perception, exhibits a higher prevalence (41.3%) compared to ageusia (28.0%) and hypogeusia (33.5%) among patients with COVID-19 infection. The exact mechanisms underlying the differential presentation of taste disorders in these patients remain uncertain, but several potential explanations exist. All three types of taste disorder could arise from damage along the central taste pathway, involving areas such as the brainstem, thalamus, cranial nerves, or cerebral cortex. Previous evidence suggests that cerebral involvement in COVID-19 may occur during both early and late stages of the infection.

In April 2020, 88% of a series of over 400 COVID-19 disease patients in Europe were reported to report gustatory dysfunction (86% reported olfactory dysfunction).[7]

Other causes[edit]

Local damage and inflammation that interferes with the taste buds or local nervous system, such as that stemming from radiation therapy, glossitis, tobacco use, or the wearing of dentures, can also cause ageusia. Other known causes include loss of taste sensitivity from aging (causing a difficulty detecting salty or bitter taste), anxiety disorder, cancer, kidney failure and liver failure.

Saliva and Ageusia[edit]

Taste sensation is produced when volatile substances come in contact with taste bud receptors. Taste buds are mainly present on the tongue papillae in proximity to the minor salivary glands. Salivary fluids dissolve the food particles and bathe the taste buds, initiating taste perception. Saliva is considered to protect and modulate taste sensation through receptors.[8]

Zinc[edit]

Zinc deficiency is linked with hyposalivation and taste changes. It is reported that deficiency of a zinc-binding protein, Gustin, is linked to taste bud abnormalities. A global oral sensitivity molecule, 6-n-propylthiouracil was recently reported to be inversely related to zinc concentration in saliva, associated with polymorphism of gustin gene. Moreover, hypogeusia or ageusia is also associated with low levels of cAMP (cyclic adenosine monophosphate) and cGMP (cyclic guanosine monophosphate) in the saliva, as cAMP is a possible growth factor for taste buds. cAMP and cGMP play a critical role in chemosensory transduction. cGMP is suggested to be vital in interaction with Ca and proteins in signaling of the gustatory and olfactory systems. A cAMP-activated protein kinase acts as a nutrient and sensor in the hypothalamus, and it activates cell surface and send signals in association with G proteins.[8]

Diagnosis[edit]

Ageusia is diagnosed by an otolaryngologist, who can evaluate a patient's loss of taste among other things. To do this, a specialist will look into any other factors that could be causing ageusia, such as examining the head, nose, ears, and mouth. An otolaryngologist can also conduct a series of tests to assess the severity of ageusia, which includes identifying specific tastes that the patient can sense or recognize.[9][10]

Treatment[edit]

Antihistamines, decongestions and antibiotics can be used to treat ageusia.[3]

Complications[edit]

Ageusia and other taste disorders can negatively impact health and the overall quality of life.[11]

Only rarely life threatening, taste problems can be a major cause of day-to-day discomfort and can result in serious psychological and medical difficulties. Many individuals with taste disorders come to believe their disorder is unique to them, a belief that is fostered by the lack of appreciation and knowledge of such problems on the part of others, often including members of the medical establishment. When taste sensations are lacking, decreased, or distorted, many persons become depressed, reduce their social activities, and alter their food habits in unhealthy ways. Some lose weight because food is no longer appealing. Others gain weight by increasing their intake of crunchy junk foods. Still others use too much sugar or salt – behaviors that can be particularly problematic to diabetics or persons with hypertension. Because taste buds within the larynx and oropharynx can activate reflexes that prevent aspiration, persons lacking taste in these regions, such as some of the elderly, can suffer from such problems.[11]

References[edit]

  1. ^ "Taste Disorders". Massachusetts Eye and Ear Infirmary. Retrieved 30 November 2018.
  2. ^ a b Hummel T, Landis BN, Hüttenbrink KB (2011). "Smell and taste disorders". GMS Current Topics in Otorhinolaryngology, Head and Neck Surgery. 10: Doc04. doi:10.3205/cto000077. PMC 3341581. PMID 22558054.
  3. ^ a b c d "Ageusia (Loss of Sense of Taste): Definition, Causes & Treatment". Cleveland Clinic. Retrieved 2024-04-14.
  4. ^ Al-Ani RM, Acharya D (August 2020). "Prevalence of Anosmia and Ageusia in Patients with COVID-19 at a Primary Health Center, Doha, Qatar". Indian Journal of Otolaryngology and Head and Neck Surgery. 74 (Suppl 2): 2703–2709. doi:10.1007/s12070-020-02064-9. PMC 7435125. PMID 32837952.
  5. ^ Vaira, Luigi; Salzano; Deiana; De Riu (2020). "Anosmia and Ageusia: Common Findings in COVID-19 Patients". The Laryngoscope © 2020 the American Laryngological, Rhinological and Otological Society, Inc. 130 (7): 2. doi:10.1002/lary.28692. PMC 7228304. PMID 32237238. ProQuest 2398912838 – via ProQuest.
  6. ^ a b Saniasiaya, Jeyasakthy; Islam, Md Asiful; Abdullah, Baharudin (July 2021). "Prevalence and Characteristics of Taste Disorders in Cases of COVID‐19: A Meta‐analysis of 29,349 Patients". Otolaryngology–Head and Neck Surgery. 165 (1): 33–42. doi:10.1177/0194599820981018. ISSN 0194-5998.
  7. ^ Lechien JR, Chiesa-Estomba CM, De Siati DR, Horoi M, Le Bon SD, Rodriguez A, et al. (August 2020). "Olfactory and gustatory dysfunctions as a clinical presentation of mild-to-moderate forms of the coronavirus disease (COVID-19): a multicenter European study". European Archives of Oto-Rhino-Laryngology. 277 (8): 2251–2261. doi:10.1007/s00405-020-05965-1. PMC 7134551. PMID 32253535.
  8. ^ a b Abduljabbar, Tariq; Alhamdan, Rana S.; Al Deeb, M.; AlAali, K.; Vohra, F. (2020). "Association of Salivary Content Alteration and Early Ageusia Symptoms in COVID-19 Infections: A Systematic Review". European journal of dentistry. 01 (14). doi:10.1055/s-0040-1716986. PMID 33242917.
  9. ^ "Ageusia: Causes, Symptoms And Treatment". Netmeds. Retrieved 2021-03-26.
  10. ^ "Taste Disorders: Get Facts About Causes, Treatment & Symptoms". MedicineNet. Retrieved 2021-03-26.
  11. ^ a b Doty, R.L. (2014). Aminoff, Michael J. (ed.). Ageusia (Encyclopedia of the Neurological Sciences 2nd ed.). Academic Press. pp. 69–71. doi:10.1016/B978-0-12-385157-4.01112-X. ISBN 9780123851581.

External links[edit]

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