Severe Late-Onset Drug-Induced Immune Thrombocytopenia Following IFN β -1a Treatment: A Case Report of a 52-Year-Old Woman with Relapse-Remitting Multiple Sclerosis.

Interferon β -1a (IFN β 1a) is considered safe in relapsing-remitting multiple sclerosis (RRMS). Drug-induced thrombocytopenia (DITP) is a rare but underreported adverse event that is often confused with other causes of thrombocytopenia. We report the case of a 52-year-old woman who developed limb and oral mucosa petechiae and hematochezia, 10 years after beginning IFN β 1a. Blood work showed an isolated severe thrombocytopenia and ruled out other autoimmune diseases, viral infections, intravascular hemolysis, and renal impairment. Oral corticosteroids and tranexamic acid were initiated with a favorable platelet response. IFN β 1a was resumed, leading to recurrence of thrombocytopenia. Platelets came back to normal after intravenous immunoglobulins and IFN β 1a was definitively discontinued. To our knowledge, this is the first case of drug-induced immune thrombocytopenia (DITP) associated with IFN β 1a.