An abnormal immune response masquerading as infectious conditions.

Kikuchi-Fujimoto disease (KFD) is a rare, benign, self-limited lymphadenitis most commonly affecting children and young adults, particularly females of Asian descent. Its etiology is unclear but is thought to involve immune dysregulation triggered by infection. We report a 14-year-old South Asian female presenting with 8 days of high fever, frontal headache, bilateral eye redness, transient arthralgias, and palpable lymphadenopathy in the cervical, axillary, and supraclavicular regions. Her history included recent travel to multiple countries and a prior episode of fever of unknown origin attributed to Bartonella. Initial laboratory evaluation revealed pancytopenia, elevated transaminases, and increased erythrocyte sedimentation rate and lactate dehydrogenase with normal C reactive protein. Infectious workup was negative for malaria, cytomegalovirus, West Nile virus, Rickettsia, Bartonella, and dengue. Ultrasound of the left axilla and computed tomography showed bilateral axillary lymphadenopathy. A cytokine panel demonstrated markedly elevated IL-18. Definitive diagnosis was established by axillary lymph node biopsy, which revealed histiocytic necrotizing lymphadenitis consistent with KFD. Systemic inflammatory disorders such as systemic-onset juvenile idiopathic arthritis, multisystem inflammatory syndrome in children, and Kawasaki disease were considered and excluded based on clinical, laboratory, and histopathological findings. The patient's fever resolved after dexamethasone administration, supporting an immune-mediated process. She subsequently developed recurrent fever, rash, and oral ulcers, which responded rapidly to intravenous corticosteroids, followed by a steroid taper.