A case of multicentric reticulohistiocytosis.

Multicentric reticulohistiocytosis (MRH) is a rare non-Langerhans histiocytosis of unknown etiology with a predilection for joint and skin. The characteristic clinical features are papulonodular skin eruptions and inflammatory polyarthritis, sometimes progressive to arthritis mutilans, a severe destructive arthropathy. Although these manifestations can present at the same time, it is more common that one feature precedes the others. Notably, these features are similar to those found in some rheumatic diseases, such as rheumatoid arthritis or dermatomyositis, and this can lead to a misdiagnosis, especially during periods where only one feature is present. Herein, we report a female patient with polyarthralgia and subsequent skin eruptions, who was eventually diagnosed with MRH. Her symptoms seemed to resemble those of some rheumatic diseases, but several features such as affected joints and the characteristic shape of the skin lesions did not correspond to that. The histological result of infiltration of histiocytes and multinucleated giant cells in the skin ultimately facilitated the correct diagnosis. In this paper, we review MRH briefly and highlight several differential points which enable us to increase the likelihood of correctly diagnosing MRH.