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Differential Diagnosis

Serological testing should separate toxoplasmosis from other entities. However, positive serology will not differentiate acute disease from simple exposure and previous infection. The majority of patients with toxoplasmosis seen by radiologists will be in the immunocompromised/AIDS group. AIDS and its various disease manifestations are quite different in tropical and developing countries compared with industrialized nations (see Chapter on AIDS). Toxoplasmosis in the immunocompetent individual is so clinically nonspecific that it may at first be overlooked. Some studies of epidemic toxoplasmosis suggest that symptoms may in fact be quite common but are simply not recognized.

The two most common diseases to simulate toxoplasmosis are infection with the cytomegalovirus and the Epstein-Barr virus. Both can present with fever, lymphadenopathy, fatigue, and splenomegaly. In congenital toxoplasmosis, the classic clinical and radiographic tetrad of diffuse intracranial calcifications, choroidoretinitis, hydrocephalus or microcephaly, and psychomotor retardation strongly suggests the diagnosis. The combination of multiple small calcifications in the brain parenchyma together with involvement of the basal ganglia in a neonate is highly suggestive of toxoplasmosis. Cytomegalovirus disease will provide the main diagnostic imaging challenge because the radiographic appearances of the intracranial calcifications may be quite similar.

Other causes of intracranial calcification in the newborn or young child, such as tuberculomas, hemangiomas, and neoplasms, are more easily differentiated on imaging, and the clinical presentation is also usually different. Occasionally, in toxoplasmosis a curvilinear calcification measuring as much as 19-mm in length may be somewhat suggestive of a cyst (e.g., echinococcosis), but almost invariably there will be other calcifications in the brain more indicative of toxoplasmosis.

Good clinical correlation is essential for the accurate diagnosis of both congenital and acquired toxoplasmosis. In adults, particularly, knowledge of the immune status of the patient is very important.

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Copyright: Palmer and Reeder