Malignant lymphoma simulating lymph node toxoplasmosis.

On histological examination of 667 cases originally suspected of lymph node toxoplasmosis, 12 cases were diagnosed as malignant lymphoma and 15 cases as atypical hyperplasia (AH), suspicious of malignant lymphoma. All 12 malignant cases were of Hodgkin's disease: eight of the lymphocyte predominant nodular type, two of lymphocyte predominant diffuse type, and two of the nodular sclerosis type. In all cases, the lymph nodes contained small groups of epithelioid cells which were virtually indistinguishable from those seen in toxoplasmosis. In the differential diagnosis between lymph node toxoplasmosis and malignant lymphoma, the following features were found helpful. In toxoplasmosis the general structure is preserved and germinal centres are frequent, while in malignant lymphoma and in AH the general structure is destroyed. However, in some cases of toxoplasmosis germinal centres may be difficult to identify because their margins are indistinct due to clusters of epithelioid cells. Also, in some types of Hodgkin's disease and in some cases of AH with epithelioid cells, the general structure of the lymph node may be partially preserved. The occurrence of epithelioid cells within germinal centres seems to be a specific feature for toxoplasmosis; it was never seen in malignant lymphoma nor in AH. The occurrence of strands of monocytoid cells (unreife Sinushistiocytose) though a fairly typical feature of toxoplasmosis, was also occasionally seen in Hodgkin's disease or AH.