Lambda immunoglobulin light chain restricted B cells in the ascitic fluid in association with terminal ileal florid follicular hyperplasia

Distinguishing reactive changes from neoplastic processes during lymphoid tissue evaluation is oftentimes difficult. Ancillary studies, such as flow cytometry, may aid the diagnosis by demonstrating monotypic or polytypic light chain expression on the B cells. The detection of immunoglobulin light chain restricted B cell population is considered a surrogate marker of clonality, which can be confirmed by molecular assays. In general, the presence of a monotypic B cell population in the ascitic fluid is considered lymphomatous involvement rather than a reactive condition. We describe a young, previously healthy male patient who developed ascites with a lambda light chain restricted B cell population. Further investigation revealed florid follicular hyperplasia, histologically mimicking diffuse large B cell lymphoma, in the terminal ileum. Follicular hyperplasia in the gastrointestinal tract with lambda light chain restricted B cells has been recently described in the pediatric population. Importantly, our case demonstrates that such entity can occur in older age groups. This recognition could prevent misdiagnosis and unnecessary treatment in similar cases.