Ageusia ( ) is the loss of
taste functions of the
tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and
umami (the taste of
monosodium glutamate). 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 aguesia is relatively rare compared to
hypogeusia — a partial loss of taste — and
dysgeusia — a distortion or alteration of taste.
Diagnosis
In order to discover the extent of the ageusia, a scientist attempts to discern the minimum level of a chemical that a patient can detect by taste. Patients may also be asked to compare various concentrations of chemicals in order that the doctor may ascertain what level of intensity that the patient can differentiate. Various methods are used, including the "sip, spit, and rinse" test as well as direct application of chemicals to the tongue.
Causes
Neurological damage
Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the
lingual nerve and the glossopharyngeal nerve. The lingual nerve passes taste for the front two-thirds of the tongue and the glossopharyngeal nerve passes taste for the back third of the tongue. Neurological disorders such as
Bell's palsy,
Familial dysautonomia, and
Multiple sclerosis cause similar problems to nerve damage, as do certain
infectious conditions like
primary amoeboid meningoencephalopathy. 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.
Problems with the endocrine system
Deficiency of
vitamin B
3 (
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 and
zopiclone.
Other causes
Local damage and inflammation that interferes with the taste buds or local nervous system such as that stemming from radiation therapy,
glossitis,
tobacco use, and denture use also cause ageusia. Other known causes include loss of taste sensitivity from
aging (causing a difficulty detecting salty or bitter taste),
anxiety disorder,
cancer,
renal failure and
liver failure.
Sources
MedTerms Online Medical Dictionary. "Ageusia". Retrieved April 15, 2005.
Family Practice Notebook. "Taste Sensation". Retrieved April 15, 2005.
Massachusetts Eye and Ear Infirmary. "Taste Disorders". Retrieved May 26, 2010.
Category:Gustatory system
Category:Laryngology
