Kikuchi-Fujimoto Disease Complicated with Reactive Hemophagocytic Lymphohistiocytosis.

Kikuchi-Fujimoto disease (KFD) is a benign cause of self-limiting subacute necrotizing lymphadenitis. KFD is rarely complicated with reactive hemophagocytic lymphohistiocytosis (HLH), and the clinical features of the simultaneous occurrence of these conditions are uncertain. A 30-year-old Japanese man with a persistent fever and sore throat presented to our hospital for treatment. Laboratory analysis showed bicytopenia, and radiological studies showed systemic lymphadenopathy accompanied by splenomegaly. A bone marrow examination showed hemophagocytic macrophages, suggesting HLH. Malignant lymphoma was suspected as a possible underlying disease, but the histology of the lymph nodes led to a final diagnosis of KFD and treatment with prednisolone (1 mg/kg/day), resulting in clinical improvement. This case highlighted the importance and difficulty of differentiating KFD from malignant lymphoma as an underlying condition of HLH. The literature review showed that patients with HLH-associated KFD may have higher serum ferritin and lactate dehydrogenase levels compared to typical KFD cases. Definite diagnosis based on pathological examination is essential for a better understanding of this rare disease. The presence of systemic lymphadenopathy does not exclude the possibility of KFD. This case serves to remind physicians that KFD is a potential etiology of HLH.