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.