Histological and immunohistochemical features of the spleen in persistent polyclonal B-cell lymphocytosis closely mimic splenic B-cell lymphoma

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/5329558967545656 webcitePersistent polyclonal B-cell lymphocytosis (PPBL) is a rare clinically benign lymphoproliferative disorder first described by Gordon et al. in 1982 [1]. To date, around 200 cases worldwide have been reported in literature. PPBL is characterized by chronic mild-to-moderate peripheral polyclonal lymphocytosis of B cell origin as evidenced by flow cytometry and variable number of atypical binucleated lymphocytes present on peripheral blood film. The total lymphocyte count is not always elevated in all patients. Due to the hallmark presence of binucleated lymphocytes, this entity is also called B-cell lymphocytosis with binucleated lymphocytes. The majority of patients also demonstrate polyclonal increase in serum IgM. It is most frequently reported in young or middle-aged female smokers [1-6]. Most patients present with mild nonspecific symptoms, such as weakness and fatigue. Mild splenomegaly is a single most frequently reported clinical finding, present in about 10% of patients according to the largest case series [2]. Massive splenomegaly has been only rarely reported in the literature. As most patients have an indolent clinical course and peripheral lymphocytosis is sometimes absent, this condition is likely under-recognized. PPBL resembles malignant lymphoproliferative disorder in many aspects, both morphologically and at the molecular/cytogenetic levels. In addition to the hallmark atypical lymphocytes, the bone marrow of these patients sometimes shows intrasinusoidal distribution of B lymphocytes resembling marrow involvement by splenic marginal zone lymphoma [7]. We here report histological and immunohistochemical features of the spleen in a young female with PPBL who underwent splenectomy due to progressive splenomegaly on her 6th annual follow-up. Very recently, Italian investigators Del Giudice et al. described similar histopathologi