Drug reaction simulating malignant lymphoma: a case due to pyrimethamine.

A 9 1/2-year-old boy who had been treated with pyrimethamine and sulphadimidine presented with generalised lymphadenopathy, fever, and an unusual sun-tanning. He was found to have mild anaemia, severe leucopenia and thrombocytopenia. The bone marrow was megaloblastic. Lymph node biopsy was initially interpreted as showing malignant lymphoma. No treatment for neoplasia was given and he was well 4 1/2 years later. We consider that the seemingly malignant changes were due to pyrimethamine.