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The occurrence of more than one distinct form of an organism in a single life cycle.



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.


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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References in periodicals archive ?
Malignant Epithelial Cells arranged Singly with Marked Nuclear Pleomorphism with Prominent Nucleoli (FNAC-Pap) 40X
The differential diagnosis for an oncocytoma on biopsy includes an eosinophilic variant of chromophobe renal cell carcinoma, which has a more solid architecture, subtle nuclear irregularity and pleomorphism, flocculent cytoplasm, and perinuclear haloes (B), and a papillary renal cell carcinoma, for which subtle papillary architecture and hemosiderin are often present (C).
A central single assessment of less than 1/400 of the total number of endothelial cells in an eye with keratoconus may miss polymegathism, pleomorphism, and endothelial cell damage in the region of eccentric cone since the sample observed might not be representative.
A slight pleomorphism was observed, although no atypical mitosis and necrosis were identified.
Even though its pleomorphism implies the possibility of malignancy, it carries a good 5-year prognosis when compared with diffuse infiltrative astrocytomas.
These cells are characterized by polymegathism (cell size variability) and pleomorphism (cell shape variation).
Histological features significantly associated with higher tumor grade included increase in nuclear pleomorphism (p value=0.
Pleomorphism, bizarre cells, and a high mitotic index were consistent with malignant behavior.
Connective tissue capsule exhibits presence of numerous spindle shaped cells exhibiting nuclear hyperchromatism and pleomorphism (figure 5).
Microscopically, the tumor consisted of spindle cells arranged in bundles or incidentally, with elongated, oval, or thickened, hyperchromatic nuclei, with pleomorphism.
As with most histologic specimens, presence of the following increases likelihood of malignancy: necrosis, spindling, vesicular nuclei with large nucleoli, increased mitotic activity, high nuclear to cytoplasmic ratio, and pleomorphism.
Necrosis, nuclear pleomorphism, and mitotic activity were not detected.