A review is presented of the drug-induced gustatory disorders that have so far been identified. Metallic, bitter or salty phantogeusias and hypogeusias, often of a dissociated type, which may even develop into ageusia have been described as side effects of treatment with some drugs. Personal observations on six cases are reported in which the gustatory disorders are attributed to the ingestion of phenylbutazone, carbamazepine, chlormezanone and baclofen. After interruption of the treatments these disorders were reversible within weeks to months.
The multiple variations of the course of the gustatory nerves still considered possible are discussed. Recent investigations lead to the conclusion that there is only one path for the gustatory fibers for each gustatory area: 1) from the anterior part of the tongue via the tympanic cord and facial nerve to the medulla oblongata; 2) for the posterior part of the tongue in the IX cranial nerve; and 3) from the soft palate via the greater superficial petrosal nerve to the facial nerve. The trigeminal nerve carries no gustatory fibers to the brain.
In a first anatomical section the peripheral gustatory pathways, their central connections, nuclei and cortical projections are discussed. It is evident, that the gustatory fibres from the posterior part of the tongue run in the IX nerve and those from the soft palate reach the medulla oblongata via the petrosal and facial nerve. For the anterior part of the tongue there obviously exists only one gustatory pathway via the chorda tympani-facial nerve. About the further central pathways of taste fibres is much less known. In a second part the methods of taste testing with different taste solutions and the electrogustometry are described. Their practical use and the pitfalls of testing are considered. The disorders of the taste sense compose a third part. Genetic and endocrine abnormalities as well as the side effects of drugs and radiotherapy and the destruction of taste nerves may lead to gustatory deviations. The possibility of central gustatory disorders, especially the combined loss of taste and smell as a result of trauma are mentioned. A chapter dealing with the therapy of taste disorders and a short outlook on the genetic aspects of this oral sense complete this review.
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