Immunocytometry and gene rearrangement analysis in the diagnosis of lymphoma in an idiopathic pleural effusion.

We report a patient with an idiopathic pleural effusion in whom the diagnosis of non-Hodgkin's lymphoma was established by immunocytometry of pleural fluid and confirmed by the detection of B-cell immunoglobulin gene rearrangement. Immunocytometry is a rapid, semi-automated laboratory method for phenotyping lymphoid cells by determining immunoglobulin and other cell surface antigen expression. This method defines the cell lineage (T or B cells) and the clonality (monoclonal or polyclonal) of a population of lymphocytes. The presence of a monoclonal population of lymphocytes can also be confirmed by recently developed molecular biologic techniques (e.g., Southern blotting) that provide the ability to detect rearrangements of the genes that encode either B-cell immunoglobulin proteins or T-cell antigen receptor proteins. To our knowledge, this case represents the first reported application of immunophenotypic and gene rearrangement analysis in a previously undiagnosed pleural effusion to establish the diagnosis of lymphoma. These relatively new laboratory methods may have a role in the evaluation of idiopathic lymphocytic pleural effusions.