Answer: Angioimmunoblastic T cell lymphoma

Histology: The lymph node shows near complete effacement of architecture by a polymorphous lymphoid infiltrate embedded within a vascular rich matrix. Focally the infiltrate extends outside the lymph node capsule. Despite the degree of involvement, the subcapsular sinuses are focally patent as well. On higher power, the infiltrate is an admixture of small lymphocytes, immunoblasts and plasma cells with scattered eosinophils. In areas the lymphocytes are enlarged and have abundant clear cytoplasm, and these cells grow in a sheet like fashion in between the prominent high endothelial venules. Immunohistochemical studies showed the lymphocytes to be T-cells with the following phenotype: CD3+, CD4+, CD10+, and Bcl-6+. CD21 shows extrafollicular expansions of follicular dendritic cells along the high endothelial venules.

Discussion: Angioimmunoblastic T-cell lymphoma (AILT) is one of the more commonly encountered recognized entities in the T-cell lymphoma category, representing 15-20% of peripheral T-cell lymphomas, but representing only 1-2% of all NHL’s in the US. The disease is typically seen in late middle age to elderly, often presenting with generalized lymphadenopathy and hepatosplenomegally. Skin rash and bone marrow involvement are also frequent occurrences. One of the more common clinical laboratory findings is hypergammaglobulinemia, which is typically polyclonal in nature but which may occasionally be a monoclonal IgM or much more rarely produce a small monoclonal IgG spike, as was observed in this case. Circulating autoantibodies and hemolytic anemia are also commonly observed. The immunophenotype suggests that this lymphoma is derived from germinal center T-cells, which share the markers CD10 and Bcl-6 with germinal center B-cells. Another peculiar feature of this lymphoma is the homing of follicular dendritic cells to the perivenular location which is mediated by CXCR13. The prognosis is poor, with a median survival of less than 3 years.