Ageusia refers to a complete loss of taste. In instances where it is partial it is then falls under the spectrum of the conditions such as
hypogeusia (decreased sensitivity to all tastants)
hyperguesia (enhanced gustatory sensitivity)
dysgeusia (unpleasant perception of a tastant) and
When loss of sensation only involves half of the tongue it is then termed hemiageusia.
In may occur on its own or concomitantly with other deficiencies such as anosmia.
Pathology
Ageusia may result from variable pathology which includes:
midbrain and thalamic infarction 1
dietary deficiencies
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systemic conditions
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cranial nerve lesions affecting gustatory function
neuritides: due to conditions such as herpes zoster
dissection of cervical arteries
space-occupying processes in the cerebellopontine angle (meningioma or neurinoma)
neoplastic lesions affecting the skull base
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iatrogenic
following laryngoscopic manipulation
skull trauma
following resection of intracerebral tumors 4
medications 5
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infections
COVID-19 2,3
polyneuropathies (due to conditions such as diphtheria, porphyria, lupus, or amyloidosis)