The histological diagnosis of toxoplasmic lymphadenitis.

The commonest presenting sign of acquired toxoplasmosis in man is enlargement of superficial lymph nodes. The persistence of the nodes may lead to a suspicion of malignant lymphoma and the diagnosis then hinges on the lymph node biopsy. Three cases of toxoplasmic lymphadenitis are described in each of which the diagnosis was unsuspected clinically. The chance discovery of a toxoplasma cyst in the lymph node section of Case 1 led to the correct diagnosis, after an initial diagnosis of Hodgkin's disease had been made. In the other two, strikingly similar histological changes in the lymph node biopsies suggested the diagnosis, which was confirmed serologically in each case. The histological changes are described and the clinical and pathological aspects of toxoplasmic lymphadenitis are briefly reviewed, with special reference to the differentiation from malignant lymphomatous conditions and to the specificity of the histological picture. It is concluded that the histology is, in many instances, sufficiently distinctive for a tentative diagnosis of toxoplasmic lymphadenitis to be made on the lymph node biopsy. The diagnosis should always be confirmed by isolation of the parasite or by serological tests. It is exceedingly rare for toxoplasma cysts to be found in lymph nodes and only one previous observation of this kind has been reported.