A Al-Shehri. Taste Disturbance Because Of Drug Therapy Or Systemic Diseases. The Internet Journal of Otorhinolaryngology. 2002 Volume 2 Number 1.
Disturbance of taste does not often appear in dayly practice  and mostly is an transient disorder within cold diseases. Permanent loss or disturbance of taste, however, is followed by a fatal impairment of quality of life, as eating and drinking practice changes thoroughly. The patient is no longer able to realize aromatics and cannot recognize inedible or spoiled food.
Besides of local processes and disturbances of cerebral nerves specific symptoms of taste disorders can be guiding to a systemic disease or to side effects of drug therapy in the treatment of systemic diseases.
In the diagnostic of dysgeusia we have to distinguish between
quantitative dysgeusia: ageusia (total loss of taste) of hypogeusia (attenuation of taste) for some or all aromatics or taste qualities
qualitative dysgeusia als false interpretation of the applied aromatics (parageusia).
Within diagnostic measures the patient's history often leads to correct diagnosis. The posed questions concerne diseases of the nose and the nasal sinus, recent virus infections, allergies, contaminant load within the area of the place of employment (e.g. vapor), intake of drugs etc (s. Tab. 1).
Many people cannot distinguish between disturbances of taste or smelling, they actually realize, that they cannot taste anymore . So the physician should give the patient an example, how to distinguish the two senses: e.g. in coffee the bitters can be tasted, but the aromatics can be smelled, and both of them lead to the specific stimulant. With questions for the realization of intensive odours as e.g. garlic, perfumed soap and cooking odours the physician can find out, whether the patient cannot smell anything of if smelling only is reduced.
Standardised measures to proove the sense of smell and taste are still not available. There are several test-sets, which still are very expensive and take a large expenditure of time . (The basic equipment of Cobal costs about 180 DM with a durability of one year.)
Gustometry is done by application of supraliminal solutions of salt, sugar, citric acid and chinin sulfate via spray, drops, paper sheets of capsula, being applied globally or on one side each. The application form of gustometry, however, is not yet standardized . Electrogustometry is done in cases of expert appraisement.
In many cases
Local symptoms of the head
As smell is involved in all sensations of taste, diseases of the mouth as well as diseases that cause disturbance of smelling can lead to taste differences. In most cases there are viral and bacterial infections with rhinitis, sinusitis, pharyngitis, stomatitis.
In case of loss of a single taste quality the identification of the injured cerebral nerve is possible because of the topography of the single taste bud and its nerval supply .Other symptoms of the oral cavity lead to systemic diseases, that may cause an affection of the cerebral nerve.
Central and peripheral disturbances of the n. trigeminus (n. mandibularis) after cerebral injury, esp. of the skull base of the ethmoidal labyrinth, of the n. olfactius or bulbus, as well as tumors of the anterior calvaria (e.g. olfactorius menigeoma), peripheral facial lesions within the pars mastoidea can also cause taste disturbances.
Paroxysmal abnormal sensations of taste or smell after head injury can be a symptom of temporal lobe epilepsia.
Taste disturbances can be found in case of many cerebral processes as e.g. meningitis, encephalitis, injury of the medulla oblongata of the thalamus as well as lesions of the cerebral cortex.
Systemic diseases causing taste disturbances
Drug induced taste disturbance: There are many drugs that can induce a mainly reversible disturbance of taste (s. Tab. 4a, 4b).
Intoxications: Intoxication with trichlorethylen, stilbamidin, allopurinol can cause a peripheral leasion of the n. mandibularis (V3). Carbon monoxide poisoning can be followed by central dysgeusia .
Physiological changes of taste caused by hormonal changes and aging appear very often. Even isolated ageusia concerning one single substance, e.g. in bakers, cooks and perfume producers, are quite common .
In about 70 % [2, 3] pathologic disturbances of taste are caused by diseases of the smelling system. Therefore differential diagnosis should always include the olfactorial parameters to delimit a pure taste disturbance from nasal diseases. These patients must be instructed about the causality of their supposed taste disturbance, as they often do not understand the causal relationship.
As the taste disturbance is not a monocausal disease, there is no causal therapy. First of all causal agents have to be eliminated resp. treated. These measures include the reduction of drug side effects, the improvement of antidiabetic treatment and elimination of noxious agents. Some authors demand for substition of high dosages of vitamine B and A or zinc  if deficiency is proved, wereas the prove of these substances is not part of the routine diagnostics. In the treatment of diseases, which are associated with these deficiencies, as e.g. chronic liver diseases or alcohol abuse, the authors require a substition of vitamine B and zinc even without the expensive diagnostic of trace materials.
In the treatment of ageusia substituion of zinc is successful even in those cases, in which deficiency of zinc was not proved. Some authors think the concentration of zinc in the reserve proteins having direct influence on the sensitivity of the taste buds, as in patients with hypogeusia a deficiency of zinc in the reserve proteins could be proved. Latent intracellular zinc deficiency in the oral mucosa may be compensated by high dosages of zinc [1, 2, 3].
In most cases there is a passagere manifestation of taste disturbance, that disappear with the healing of the systemic disease or that in cases of central disturbances of the nerval system can be compensated (by learning effects?)
However, a permanent manifestation of taste disturbance is a fatal disorder, as it has a severe influence on eating and drinking conditions, changing the quality and amount of food intake as well. There are only few possibilities to compensate this loss. Especially in elderly or lonesome patients, who are not able to look after themselves sufficiently, the combination of inappetence and loss of taste may lead to severe nutrition disorder. In these cases the exact differential diagnosis of the remaining and disturbed taste is essential, as to offer the patient a diet that may compensate nutrition deficiencies in consideration of the remaining taste qualities. For these patients, an individual nutrition plan must be developped with the help of a qualified diatician, including the patient's preferred food and the remaining taste qualities as well, securing a balanced alimentation.
Dr. A. Wegener, Buschweg 39a, D-53229 Bonn, Germany e-mail: firstname.lastname@example.org