A case of hemophagocytic lymphohistiocytosis with a significant response to baricitinib: a first report with review of literature.

Hemophagocytic lymphohistiocytosis (HLH) is a febrile disease with hyperinflammation characterized by activated macrophages with phagocytosis. The treatment strategy of secondary HLH has not been clearly established. Because of the high mortality rate and poor prognosis of HLH, alternative treatment strategies have been sought in treatment-resistant cases. Recently, there have been several reports that ruxolitinib, a Janus kinase (JAK) 1/JAK2 inhibitor, was effective against secondary HLH. Since the pathogenesis of HLH involves the overproduction of cytokines and JAK transmits a variety of cytokine signals, JAK inhibitors are thought to be effective in HLH. We herein report a case of HLH that was refractory to glucocorticoids, cyclosporine, and etoposide but responded to baricitinib. In the field of rheumatology, treatment-resistant cases of secondary HLH remain unmet needs. This is the first report to show that baricitinib was effective in a case of HLH. The accumulation of more cases in the future may prove that baricitinib is a potent agent for treating HLH.