A morphologic study of opportunistic cerebral toxoplasmosis.

The morphology of toxoplasma and its interaction with the cellular elements of the brain were studied in a patient who dies of extensive cerebral toxoplasmosis superimposed on Hodgkin's disease. The cerebral lesions were devoid of inflammatory cellular response and contained numerous organisms mostly in isolated multiplying forms in neurons, glia and vascular walls. Encysted forms containing multiplying organisms were seen infrequently. Intracellular parasite was identified in normal-appearing neuropil. The mode of multiplication and cyst formation of toxoplasma appeared basically similar to that described under experimental conditions. In addition, a rapid evolution of the cerebral lesions was suggested by computerized tomography. This study suggests that tissue necrosis in human cerebral toxoplasmosis is the result of an increased rate of multiplication and enhanced cellular invasiveness of the parasite most likely related to impaired cellular immunity as has been postulated by clinical and experimental data.