A Novel Therapy for a Rare Condition: Continuous Anakinra Infusion for a Patient With Macrophage Activation Syndrome.

Macrophage activation syndrome (MAS) is a type of hemophagocytic lymphohistiocytosis (HLH), which occurs due to excessive stimulation of the immune system. Common precipitants of MAS include disseminated infection or underlying rheumatologic disorders such as adult-onset Still's disease which is characterized as an inflammatory arthritis with daily fevers and a salmon-colored rash. We present a case of a patient with probable adult-onset Still's disease and subsequent disseminated cytomegalovirus (CMV) infection, who met the criteria for MAS based on the presence of a fever, cytopenia in multiple cell lines, elevated ferritin, presence of hemophagocytosis on bone marrow, low fibrinogen, and mild splenomegaly on physical exam. The patient responded to treatment with continuous anakinra infusion and ganciclovir for treatment of CMV. Though cytotoxic medications such as etoposide have traditionally been considered first-line treatment for HLH/MAS, interleukin-1 inhibitors such as anakinra are emerging as aless cytotoxic alternative.