[Heavy chain diseases].

Heavy chain diseases (HCD) are immunoproliferative disorders characterized by the production of monoclonal immunoglobulin molecules composed of deleted heavy chains devoid of light chains. The diagnosis is established by immunoelectrophoresis (possibly combined to immunoselection) or immunofixation. The clinicopathologic features of gamma HCD are heterogenous, often somewhat similar to macroglobulinemia. Some patients show no evidence of underlying malignant lymphoproliferation. Autoimmune disorders are frequent. mu HCD is rare and often presents as chronic lymphocytic leukemia with hepatosplenomegaly and vacuolated plasma cells on bone marrow smears. Alpha chain disease is the most frequent. In its usual digestive form, the clinicopathologic pattern is uniform. The main clinical features are chronic diarrhea and severe malabsorption syndrome. At the initial stage, there is a diffuse lymphoplasmocytic infiltration of the small intestine and mesenteric nodes, sometimes reversible after treatment by antibiotics alone. At the terminal stage, a malignant lymphoma, often of immunoblastic type, occurs. The natural history and epidemiology of alpha HCD should provide insights into the pathogenesis of malignant lymphoid proliferations.