Histopathology of the Spleen in T-Cell Large Granular Lymphocyte Leukemia and T-Cell Prolymphocytic Leukemia

We review retrospectively the spleen histology in 8 patients with T-cell large granular lymphocyte (LGL) leukemia and 4 with T-cell prolymphocytic leukemia (T-PLL) to identify characteristic patterns of involvement and to distinguish such patterns from those described in other low grade B- and T-cell malignancies. Moderate splenic enlargement with red pulp expansion due to lymphocytic infiltration was characteristic of LGL leukemia. Abnormal lymphocytes expressed cytotoxic granule proteins and were consistently CD45RO and CD5 negative in contrast to normal red pulp T cells. This infiltration respected anatomic boundaries with encroachment but no invasion of white pulp areas. Unlike in hairy cell leukemia, the main differential diagnosis for red pulp lymphocytosis, the white pulp was not only preserved in T-cell LGL leukemia but showed germinal center hyperplasia with expansion of the mantle zones. By comparison, T-PLL spleens showed marked red pulp lymphoid infiltration by medium-sized cells with irregular nuclei and prominent eosinophilic nucleoli. T-PLL lymphocytes, unlike LGLs, were more invasive, infiltrating the spleen capsule as well as white pulp areas. T-cell prolymphocytes did not express cytotoxic granule proteins or NK-cell markers, were CD5+, CD45RO+ like normal spleen T cells, were CD2+, CD3+, CD45+, CD43+, TCRbeta+, but CD25-, CD30-, ALK-1-, TRAP-, DBA44-, and TdT-. Expression of CD4 and CD8 in these cells mirrored that of circulating T-PLL cells. These observations on the morphologic and immunohistochemical appearances of the spleen in T-cell LGL leukemia and T-PLL may aid diagnosis of these uncommon T-cell disorders, particularly T-cell LGL leukemia, where presentation may be cryptic and where unique pathognomonic features, are absent.