Phenytoin-induced pseudolymphoma syndrome: an immunologic study.

In vitro and in vivo immunologic studies were performed on a 28-year-old woman with phenytoin sodium-induced pseudolymphoma syndrome. During the acute phase of the syndrome, the patient appeared immunologically depressed. Six months after resolution of lymphadenopathy, repeat studies demonstrated a return to immunologic competence. In vitro studies of the patient's lymphocytes when incubated with phenytoin failed to indicate a delayed hypersensitivity reaction to the drug; These findings suggest that the patient developed a clinical lymphatic proliferation at a time when she was immunologically depressed. This may result in an increased chance of a mutant malignant clone developing at a time when the immunosurveillance system is impaired and explains why a rare patient with this syndrome may develop a frank malignant lymphoma.