Castleman Disease—Still More Questions than Answers: A Case Report and Review of the Literature

Background: Idiopathic multicentric Castleman disease (iMCD) is a rare lymphoproliferative disorder with diverse clinical presentations, often posing significant diagnostic challenges. Methods: We report the case of a 20-year-old woman who first presented with fever of unknown origin (FUO) at the age of 14, followed by the development of abdominal lymphadenopathy. We conducted a comprehensive review of her clinical course, diagnostic workup, treatment response, and outcomes. Additionally, we performed a literature review of CD focusing on pathophysiology, classification, diagnostic approaches, and treatment strategies. Results: Extensive investigations performed in the meantime excluded infectious and autoimmune causes. Histopathological analysis of the excised lymph nodes ruled out malignancy and confirmed idiopathic multicentric Castleman disease. Treatment with tocilizumab, an IL-6 receptor antagonist, resulted in rapid resolution of clinical symptoms, normalization of inflammatory markers, and sustained remission. With the final diagnosis established and treatment initiated, she was transitioned at the age of 18 from a pediatric immunology to an adult clinical immunology center. Conclusions: The presented case highlights the importance of considering iMCD in the differential diagnosis of FUO, especially in adolescents, and the efficacy of targeted therapies in managing this challenging disease. A multidisciplinary approach involving clinical, laboratory, imaging, and histopathological evaluation is essential for accurate diagnosis. IL-6 pathway inhibition represents an effective targeted therapy for iMCD, capable of inducing sustained remission in this challenging disease.