Multicentric reticulohistiocytosis: a case report with molecular analysis and discussion

Summary: Multicentric reticulohistiocytosis (MRH) is a rare non-Langerhans cell histiocytosis that affects multiple organ systems, including the skin and joints. It commonly occurs in adult females and is diagnosed based on clinical presentation with associated radiologic and histologic findings. Histologic features include an infiltrate composed of multinucleated histiocytes and giant cells with a characteristic “ground glass” eosinophilic cytoplasm. Although the exact prevalence is unknown, current literature estimates that anywhere from 300 to 400 cases have been documented since being first reported in 1937. Here we present a case of MRH in a 45-year-old female who presented with eruptive red papules on the face, neck, back, hands and arms in addition to arthritis of the wrists and hands. A punch biopsy revealed dermal multinucleated histiocytes with ground glass cytoplasm positive for CD163, and negative for SOX10, S100, BRAF, and ALK. Additional immunostains and molecular testing via next-generation sequencing are pending at the time of abstract submission. BRAF, MAP2K1, TET2, KIF5B, FGRF1, and KRAS have been suggested in prior studies as potential genetic drivers, implicating MRH as a neoplastic versus autoinflammatory disease. However, overall literature is lacking. Thus, this report will provide an updated discussion regarding the molecular underpinnings of MRH. Furthermore, the authors will examine distinguishing genetic and histopathologic differences of relevant MRH mimickers to inform practicing pathologists.