A Fatal Case of Severe Fever with Thrombocytopenia Syndrome Complicated by Hemophagocytic Lymphohistiocytosis

Abstract Severe fever with thrombocytopenia syndrome (SFTS) is a recently identified emerging viral infectious disease in China that is caused by a novel phlebovirus in the family Bunyaviridae, SFTS virus, with an average case fatality rate of 12-30%. A cytokine storm with abnormally expressed cytokine profiles is associated with the disease severity. Hemophagocytic lymphohistiocytosis (HLH) is an aggressive and lifethreatening syndrome associated with excessive immune activation. We report herein on a fatal case of SFTS complicated by HLH. Consecutive plasma exchange and immunomodulatory therapy was ineffective in our case. The pathognomonic histological feature was necrotizing lymphadenitis with massive hemophagocytosis of systemic lymphoid tissues with SFTS viruses and SFTS-RNA copies. No specific treatment of SFTS is available, and an effective treatment strategy for patients with rapidly progressing SFTS has not been established. Appropriate immunomodulatory therapy is necessary for SFTS patients complicated by HLH.