Multicentric Reticulohistiocytosis Presenting as Seronegative Erosive Inflammatory Arthritis: A Diagnostic Challenge in Rheumatology

Background To describe a rare case of multicentric reticulohistiocytosis (MRH) presenting with seronegative erosive inflammatory arthritis mimicking rheumatoid arthritis, highlighting the diagnostic challenge and importance of dermatologic evaluation in rheumatologic disorders.

Case Report A 36-year-old Hispanic female presented with a 1-year history of progressive bilateral small and large joint arthralgias involving the MCPs, PIPs, wrists, and knees. Laboratory investigations revealed negative rheumatoid factor, anti-cyclic citrullinated peptide antibody, antinuclear antibody, and HLA-B27. C-reactive protein was mildly elevated (11 mg/L), and baseline imaging was normal. The patient received sequential therapy with methotrexate, leflunomide, and biologics agents including adalimumab and JAK inhibitors (tofacitinib, upadacitinib, baricitinib) with only partial or transient responses. Over a 6-year disease course, the patient developed new erosions on serial hand radiographs and violaceous periungual macules with nodular lesions over the digits. Infectious causes were excluded. An urgent dermatology consultation was requested. Skin biopsy revealed multinucleated histiocytes and giant cells with eosinophilic, ground-glass cytoplasm—findings diagnostic of multicentric reticulohistiocytosis.[1] Given persistent disease activity, intravenous tocilizumab was initiated alongside a tapering course of prednisone, resulting in stabilization of joint symptoms and improvement in skin lesions.

Conclusion Multicentric reticulohistiocytosis is a rare systemic granulomatous disorder that may mimic seronegative erosive arthritis, often leading to diagnostic delay. Recognition of characteristic cutaneous findings and histopathologic confirmation are essential for diagnosis.[2] Reported treatments include corticosteroids, methotrexate, cyclophosphamide, and TNF inhibitors with variable benefit. Although data remain limited, biologic therapies—particularly IL-6 inhibition—appear promising for refractory disease.[3] Early dermatologic collaboration and multidisciplinary management are key to optimizing outcomes.

References [1.] Sanchez-Alvarez C. Rheumatology 2020;59:1898-1905. [2.] Tariq S. Springerplus 2016;5:180. [3.] Pacheco-Tena C. J Clin Rheumatol 2013;19:272-6.