Pleomorphism

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pleomorphism

[‚plē·ō′mȯr‚fiz·əm]
(biology)
The occurrence of more than one distinct form of an organism in a single life cycle.
(crystallography)

Pleomorphism

 

an environmentally produced change in the incidence of disease and causes of death as well as in the properties of individual diseases, that is, nosologic entities (see NOSOLOGY).

During the 20th century, extensive immunization of populations and nationwide preventive measures in economically developed countries have eradicated many infectious diseases, for example, plague and poliomyelitis, and have sharply reduced infant mortality caused by infectious diseases. Changes in living conditions have reduced the incidence of diseases that stem from nutritional deficiency, for example, avitaminoses and iron-deficiency anemia. On the other hand, the incidence of injuries, tumors, and cardiovascular and viral diseases has increased.

New hereditary and occupational diseases have resulted from such environmental changes as those that accompany the growth of the chemical industry. Therapy-induced pleomorphism is a change in the clinical picture of a disease as a result of treatment. For example, the use of drugs has led to the disappearance of severe forms of thyrotoxicosis and anemia. Similarly, tuberculous meningitis, comas in diabetes mellitus, and acute pulmonary suppuration have become rare. In leukemia, tumor cells have disappeared from bone marrow because of the use of cytostatic agents, but they multiply in the nervous system and viscera. Undesirable side effects may follow medicinal treatment, and beyond a certain intensity these constitute a drug disease. The aftereffects of gastric or cardiac surgery, for example, can also give rise to disease.

Diseases that have received a new nosologic classification because of the growth of medical knowledge should not be considered examples of pleomorphism.

REFERENCES

Davydovskii, I. V. Patologicheskaia anatomiia i patogenez boleznei cheloveka, 3rd ed., vols. 1–2. Moscow, 1956–58.
Shul’tsev, G. P. “Terapevticheskii patomorfizm.” Klinicheskaia meditsina. 1973, no. 6.
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