Multicentric reticulohistiocytosis with elevated cytokine serum levels

Multicentric reticulohistiocytosis (MRH) is an uncommon non‐Langerhans cell histiocytosis of unknown etiology. It is a multisystem disorder characterised by a papulonodular skin eruption, mainly in the extensor surfaces, and destructive polyarthritis. Histologically, either cutaneous lesions or the synovium show a dense dermal infiltrate of histiocytes and multinucleated giant cells with an eosinophilic granular material in the cytoplasm. In the immunohistochemical analysis these cells stain positively with monocyte/macrophage markers (CD68 and CD45), as well as with certain cytokines (tumor necrosis factor‐α, interleukin 1β and interleukin 6). Moreover, recent reports suggest an osteoclastic nature of the infiltrating cells, as they stain strongly with osteoclast tissue lytic markers including tartrate‐resistant acid phosphatase and cathepsin K. We report a case of MRH presenting with clinical features of dermatomyositis. Furthermore, the patient showed elevated cytokine serum levels that lowered after therapy.