Acute Hemolytic Anemia and Immune Thrombocytopenia: A Rare Case of Parvovirus B19-Induced Evans Syndrome.

Evans syndrome is a rare condition that can be seen among patients with pre-existing rheumatological disorders such as lupus, rheumatoid arthritis, or adult-onset Still's disease. There is an association between positive anti-phospholipid antibodies and the development of Evans syndrome, but the underlying pathophysiology remains unknown. To our knowledge, this is one of the few case reports to date that describes the development of Evans syndrome triggered by parvovirus B19 in patients with pre-existing positive antiphospholipid antibodies. A 47-year-old female with a past medical history of positive antiphospholipid antibodies presented with a petechial rash on the bilateral lower extremities for two days. She reported that her child had slapped cheek disease recently. Physical examination revealed a rash on the bilateral lower extremities and mucosal petechiae in the oral cavity. She was otherwise hemodynamically stable. Initial labs showed normocytic anemia and critically low platelets of less than 2 x 103/uL. The reticulocyte count was low. Other labs showed elevated lactate dehydrogenase (LDH) and low haptoglobin, which was consistent with hemolysis. The direct antiglobulin test (DAT) was positive for warm autoantibody, which further confirmed autoimmune hemolysis. The peripheral smear showed normocytic anemia with severe thrombocytopenia with scattered spherocytes. Flow cytometry showed no evidence of lymphoma. Extensive work-ups for ADAMTS13, HIV, and hepatitis were negative. The IgM titer of parvovirus B19 was significantly elevated. The patient also had positive lupus anticoagulant and positive antibodies for beta 2 glycoprotein and cardiolipin, which were initially detected many years ago, but she never had thrombotic events or recurrent pregnancy loss that would fulfill the diagnosis of antiphospholipid syndrome (APS). The diagnosis of Evans syndrome was established based on clinical evidence of autoimmune hemolytic anemia (AIHA) and immune thrombocytopenia (ITP), which developed after a recent parvovirus B19 infection. The patient was started on dexamethasone 40 mg for two days, but did not respond to steroid treatment. She was subsequently started on intravenous immunoglobulin (IVIG) treatment for three doses, and her platelet count gradually recovered before she was discharged home stable. Parvovirus B19 may contribute to autoimmune disease onset and progression through mechanisms such as molecular mimicry, immune system disruption, and chronic infection. Some viral peptides of parvovirus B19 share similar epitopes with host antigens, and the cross-reactive antibodies produced by activated B lymphocytes also bind antigens on red blood cells and platelets, causing hemolysis and thrombocytopenia. Currently, consensus recommends steroids and IVIG as first-line and rituximab as the second-line treatment.