Systemic polyclonal immunoblastic proliferation: a diagnostic review and differential diagnosis

Systemic polyclonal immunoblastic proliferation (SPIP) is a very rare, atypical expansion of plasma cells and lymphoblasts associated with an aggressive clinical presentation. The pathogenesis of SPIP is unknown and it is unclear whether these proliferations represent a clinicopathologic entity or rather a pattern of cellular proliferation. Some evidence of infection as an initiating event has been proposed. SPIP is often difficult to differentiate from other disorders, particularly in the context of an obscuring inflammatory response. Untreated or even treated cases can be fatal. The morphologic features are characterized by a pronounced proliferation of B immunoblasts and plasma cells that typically involve the blood, bone marrow, lymph nodes, spleen, thymus, liver, kidneys, thyroid, adrenal glands, and lungs. A subset of reported cases has responded well to treatment with corticosteroids alone or in combination with cytotoxic agents, showing complete remission and resolution of lymphadenopathy and normalization of peripheral blood findings. Here, we present a case of SPIP in a 58-year-old male with polyclonal plasmacytosis, hypergammaglobulinemia, diffuse lymphadenopathy, splenomegaly, and a diffuse maculopapular rash; SPIP with skin involvement is very unusual. Fortunately, our patient showed a striking response to steroids. This article provides a brief overview of the clinicopathologic features associated with this atypical lymphoplasmacytic proliferation and a review of the literature highlighting the differential diagnosis of lymphoplasmacytic disorders.