Cold Agglutinin Disease: Improved Understanding of Pathogenesis Helps Define Targets for Therapy

The last 2 decades have seen great progress in understanding the pathogenesis of cold agglutinin disease (CAD) and development of effective therapies. Cold agglutinins can cause hemolytic anemia as well as peripheral circulatory symptoms such as acrocyanosis. We distinguish CAD, a well-defined clinicopathologic entity, from secondary cold agglutinin syndrome. This review addresses the histopathologic, immune phenotypic, and molecular features that allow CAD to be classified as a distinct clonal lymphoproliferative disorder of the bone marrow, recently recognized in the WHO classification. We discuss recent data on the possible overlap or distinction between CAD and Waldenstrom's macroglobulinemia. Two major steps in the pathogenesis of CAD are identified: clonal B-cell lymphoproliferation (leading to monoclonal IgM production) and complement-mediated hemolysis. Each of these steps constitutes a target for treatment. Established as well as novel and experimental therapies are reviewed.