Overlap of Adult-Onset Still Disease and Kikuchi-Fujimoto Disease: A Case Report and Literature Review.

Kikuchi-Fujimoto disease (KFD) and adult-onset Still disease (AOSD) are two rare conditions whose association poses a significant diagnostic challenge. KFD is characterized by subacute necrotizing lymphadenitis of unknown etiology, primarily affecting young adults, and often presents with fever and posterior cervical lymphadenopathy. AOSD is a systemic inflammatory disorder of unclear origin, defined by high-spiking fever, lymphadenopathy, hepatosplenomegaly, hyperferritinemia, and leukocytosis. To date, only 15 cases of the coexistence of both conditions have been reported, providing valuable insight into their pathophysiology. We present the case of a 32-year-old Moroccan woman with prolonged fever, arthralgia, and axillary and mediastinal lymphadenopathy. After extensive evaluation, a lymph node biopsy confirmed the diagnosis of KFD, and she met the Yamaguchi criteria for AOSD. Treatment with oral prednisone was initiated, leading to rapid resolution of fever and normalization of acute-phase reactants. This case aligns with previously documented patterns in the literature, indicating a potential shared pathogenic mechanism. The lack of specific autoantibodies in these overlap cases emphasizes the need for clinicians to look for atypical clinical presentations when diagnosing these conditions. While corticosteroids have shown effective symptomatic control in the 16 reported cases, further research is necessary to explore targeted therapies, as many patients lack adequate follow-up regarding long-term management and response to treatment.