Heavy chain diseases
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These lymphoplasmacytic proliferative disorders are characterized by the uncontrolled production of abnormal (incomplete) immunoglobulin heavy chains that cannot combine with light chains to form complete Ig molecules. Specific subtypes may be identified by serum protein electrophoresis, but immunoelectrophoresis or immunofixation may also be needed to detect the variably-sized heavy chains
There are three classifications of heavy chain disease: Gamma heavy chain disease, Mu heavy chain disease, and Alpha heavy chain disease. All of these specific heavy chain diseases are coded to 9762/3. (Note that heavy chain deposition disease is not the same as HCD; the deposition term is non-reportable and would be coded 9769/1 if collected.)
Gamma heavy chain disease (Gamma HCD) is a variant of lymphoplasmacytic lymphoma (9671/3) but is a distinct and separate disease. It may involve the lymph nodes, Waldeyer ring, gastrointestinal tract, and other extranodal sites, plus the bone marrow, liver, spleen, and peripheral blood. Most patients have systemic symptoms and generalized disease, including lymphadenopathy and hepatosplenomegaly. Prognosis is extremely variable. Low-grade disease may respond to chemotherapy.
Mu heavy chain disease resembles CLL (9823/3) because of its small, round lymphocytes but it is a distinctly different entity. This is the rarest HCD. It involves spleen, liver, bone marrow, and peripheral blood. Peripheral lymphadenopathy is usually not present. Hepatosplenomegaly is frequent. The disease usually progresses slowly.
The most common HCD, alpha heavy chain disease, is a variant of extranodal marginal zone lymphoma of MALT (9699/3) but it is classified with the other HCD’s. It mainly occurs in young adults and involves the gastrointestinal tract, mainly the small intestine and mesenteric lymph nodes. Gastric and colonic mucosa may be involved. The bone marrow and other organs are usually not involved. Rare respiratory tract involvement is described. Antibiotic therapy (coded as chemotherapy) is very effective on Alpha heavy chain disease. A newer term for alpha HCD is immunoproliferative small intestinal disease (IPSID); these terms had separate codes before 2010.
Of the three different heavy chain diseases, alpha heavy chain disease is the only classification that may transform to diffuse large B-cell lymphoma (9680/3).