The heavy chain diseases: clinical and pathologic features.

Heavy chain diseases are a family of rare, systemic syndromes typically associated with or representing a variant of a B-cell neoplasm. Their characteristic feature is production of a mutated immunoglobulin heavy chain incapable of either partnering with light chains in the formation of a full immunoglobulin molecule or of being degraded by the proteasome. The abnormal heavy chain is detected in urine and/or serum without an associated light chain, a pathognomonic finding. Depending on the subtype of the altered heavy chain, these conditions can be subclassified as alpha, gamma, or mu heavy chain disease. We discuss the clinical presentation; epidemiology; laboratory, radiologic, and pathologic features; and treatment options for each of the heavy chain diseases, emphasising the importance of an accurate pathologic diagnosis and correct interpretation of immunologic studies in their identification.