Auto-immune thrombocytopenia related to interferon therapy.

A patient with renal cell carcinoma developed reversible autoimmune thrombocytopenia while receiving leukocyte interferon (IFN) and subsequently fibroblast IFN. Bone marrow biopsies and elevated platelet-associated IgG were suggestive of immune thrombocytopenia. The patient's history of exposure to IFN and exclusion of other causes are most consistent with drug-induced immune thrombocytopenia. Rechallenge with acetaminophen, the only other drug the patient was receiving concurrently, failed to induce thrombocytopenia. With IFN alpha, acute thrombocytopenia resolved within 48 h, whereas after IFN beta it was 5 wk before platelet counts returned to normal. PaIgG, however, remained elevated for up to 30 wk. Sensitive in vitro tests failed to confirm drug-dependent binding of IgG to the patient's platelets. It is suggested that this patient developed interferon-induced autoimmune thrombocytopenia.