Multicentric reticulohistiocytosis presenting with clinical features of dermatomyositis.

Multicentric reticulohistiocytosis (MRH) is a rare disorder with proliferating histiocytes that develop into multinucleated giant cells with "ground-glass" cytoplasm. The disease presents with a rapidly destructive, sometimes permanently debilitating, polyarthritis and a papulonodular eruption, generally of the face and hands. We present 3 cases of MRH in which the initial clinical diagnosis was thought to be dermatomyositis (DM). The cutaneous findings in these cases included an erythematous, predominantly photodistributed macular and papular eruption clinically consistent with DM. However, skin biopsy specimens revealed the diagnosis of MRH. This previously unreported clinical similarity between MRH and DM is significant because the treatment options and future complications vary greatly between the 2 diseases. Thus, it is important to consider the possibility of multicentric reticulohistiocytosis when evaluating a patient with the clinical diagnosis of dermatomyositis.