Hemophagocytic lymphohistiocytosis in 2 patients with multiple sclerosis treated with alemtuzumab

Alemtuzumab is a highly effective treatment of relapsing-remitting multiple sclerosis (RRMS) with a complex safety profile, including secondary autoimmunity in 40% of patients.1 We report 2 cases of hemophagocytic lymphohistiocytosis (HLH) in patients after alemtuzumab treatment of RRMS. This hyperinflammatory syndrome consists of fever, lymphadenopathy, pancytopenia, liver abnormalities, hyperferritinemia, raised soluble interleukin 2 (IL-2) receptor, and hemophagocytosis; it may be secondary to malignancies, autoimmune diseases, or infections.2 The table summarizes the diagnostic criteria for secondary HLH.