Secondary hemophagocytic lymphohistiocytosis associated with Rocky Mountain spotted fever in a toddler: A case report

A three‐year‐old boy presented with fever, maculopapular rash involving palms and soles, and hyponatremia two weeks following a tick bite. Empiric doxycycline that he was on was discontinued following negative initial rickettsial serology based on the non‐endemicity of Rocky Mountain spotted fever (RMSF) in Northeast Ohio. He demonstrated high inflammatory markers and met the criteria for hemophagocytic lymphohistiocytosis (HLH). With a working diagnosis of macrophage activation syndrome secondary to presumed systemic‐onset juvenile idiopathic arthritis (soJIA), he received HLH‐directed therapy. Rising antibody titers in convalescent sera established the diagnosis of RMSF. The patient recovered completely with HLH directed therapy and re‐institution of doxycycline. This is the first pediatric case report of Rickettsia rickettsii induced HLH demonstrating a favorable outcome despite modified therapy.