Disseminated infection to immune activation.

A 61-year-old woman with rheumatoid arthritis on chronic immunosuppression presented with fever. Laboratory studies demonstrated multiorgan failure with pancytopenia, elevation in liver function studies, and an elevated ferritin level, with a diagnosis of hemophagocytic lymphohistiocytosis confirmed on bone marrow biopsy. After initial treatment with chemotherapy, fungal blood cultures grew Histoplasma, prompting initiation of antifungal therapy, which resulted in successful treatment of Histoplasma-associated hemophagocytic lymphohistiocytosis.