Co-occurrence of Kikuchi-Fujimoto Disease, Systemic Lupus Erythematosus, and Macrophage Activation Syndrome Presenting With Acute Pancreatitis and Myositis in an Adolescent Male Patient.

Kikuchi-Fujimoto disease (KFD) is a rare, self-limiting necrotizing lymphadenitis that can mimic infection, malignancy, or autoimmune disease. Its coexistence with systemic lupus erythematosus (SLE) and macrophage activation syndrome (MAS) is uncommon and presents significant diagnostic challenges. We report a 15-year-old boy who presented with prolonged fever, generalized lymphadenopathy, cytopenias, oral ulcers, myositis, and acute pancreatitis. Laboratory evaluation revealed positive antinuclear and anti-Smith antibodies, hypocomplementemia, markedly elevated serum ferritin levels (27,650 ng/mL), hypertriglyceridemia, and hypofibrinogenemia. Lymph node biopsy demonstrated histiocytic necrotizing lymphadenitis consistent with KFD. The patient fulfilled the diagnostic criteria for SLE complicated by MAS and acute pancreatitis. Early initiation of high-dose corticosteroids, intravenous immunoglobulin, cyclophosphamide, cyclosporine, and hydroxychloroquine resulted in clinical and biochemical remission. This case highlights the importance of recognizing KFD-SLE overlap with MAS in adolescents presenting with persistent fever and cytopenias, as prompt immunosuppressive therapy can be life-saving.