Heightened Immune Response to Presumed Loxosceles reclusa Envenomation.

Loxoscelism is a systemic inflammatory reaction in response to a brown recluse spider bite (BRSB). In this case we describe a patient with a heightened inflammatory response to a presumed BRSB, with Coomb's positive hemolysis, cytoplasmic antineutrophil cytoplasmic antibody (cANCA) vasculitis, and features of hemophagocytic lymphohistiocytosis (HLH). A 24-y-old female presented with sudden pain and swelling to her lower back, nausea, fever, and tachycardia after a presumed BRSB. Hemolysis began on hospital day 3 (15.9 g·dL^-1) with a nadir on hospital day 5 (6.3 g·dL^-1). She had an lactate dehydrogenase of 1415 U·L^-1, ferritin of 15534 ng·mL^-1, persistent fever, and signs of bone marrow suppression despite hemolysis, with thrombocytopenia (100,000 μL^-1) and an inadequate reticulocyte response (1.7%) suggestive of HLH. The patient's blood was Coomb's and cANCA/antiproteinase 3 positive. She had signs of toxin-induced vasculitis, with respiratory failure requiring bilevel positive airway pressure, radiographs with bilateral pulmonary infiltrates, and a desquamating rash. She received 6 U of packed red blood cells, furosemide for pleural and pericardial effusions, antibiotics, and symptomatic treatment during the acute phase of her illness. Hemolysis improved without glucocorticoids by hospital day 6. The patient demonstrated a dysregulated immunologic and complement-mediated response to the presumed BRSB. The triad of Coomb's positive hemolysis, cANCA vasculitis, and HLH-like reaction associated with a presumed BRSB is described for the first time in the literature and brings up questions for future research regarding the role of immune modulators and complement inhibitors in the treatment of severe loxoscelism as well as the genetic factors that predispose certain individuals to such reactions.