Cutaneous plasmacytosis with mast cell infiltration.

Cutaneous plasmacytosis is a rare disorder of uncertain etiology, described mainly in patients of Japanese descent. Clinically, it is characterized by multiple pigmented papules and plaques distributed primarily on the trunk. Histopathologically, it is marked by a dense dermal plasma cell infiltrate. Here, we describe a case of cutaneous plasmacytosis in a 55-year-old Indian male who presented with hyperpigmented plaques on the body. Histopathological examination revealed dense superficial and deep perivascular and periappendageal infiltrate composed mainly of plasma cells, lymphoid follicles with reactive germinal centres, perineural distribution of plasma cells, mast cell infiltration and increased dermal small blood vessels. Immunohistochemical analysis confirmed the polyclonal nature of the plasma cells. Laboratory investigations were within normal limits, except for the presence of polyclonal hypergammaglobulinemia without any M band. There was no evidence of autoimmune disease or any infection. There was no systemic involvement in this patient. The patient was diagnosed as cutaneous plasmacytosis and advised long-term follow-up. Peculiar histopathological finding in this case of cutaneous plasmacytosis was the presence of abundant mast cells in the dermis.