Looks Can Be Deceiving: A Case Report on Multicentric Reticulohistiocytosis Successfully Treated with Rituximab.

Multicentric reticulohistiocytosis (MRH) is an idiopathic multisystemic inflammatory disease characterized by symmetric erosive polyarthritis and typical papulonodular skin lesions. MRH can be associated with autoimmune diseases, malignancy, mycobacterial infections, and hyperlipidemia, and it is important to consider appropriate screening in this population. There is no specific diagnostic laboratory test for MRH. The gold standard for diagnosis is skin or synovial biopsy, which shows characteristic multinucleated non-Langerhans giant cells and ground glass eosinophilic cytoplasm. Although the disease spontaneously remits in approximately 10 years, MRH can rapidly progress to arthritis mutilans in the majority of cases. The diagnosis and treatment are challenging due to its low prevalence and lack of robust guidelines from major rheumatological societies. Corticosteroids and methotrexate are generally first-line treatment options. However, more recently, biologic agents have been increasingly used in refractory cases with some success. Early diagnosis is crucial in preventing disease progression. We report a case of MRH in a patient whose clinical presentation mimicked rheumatoid arthritis and was subsequently treated successfully with rituximab.