Waldenström's macroglobulinemia is an immunoproliferative disorder characterized by the presence of large amounts of monoclonal macroglobulin (IgM) in the serum, apparently produced by abnormally proliferating lymphocytes.1 While in the original description of Waldenström the number of lymphocytes was not increased in the peripheral blood, the bone marrow showed characteristic lymphocytic infiltrations and in later reports on macroglobulinemia the disease was associated with peripheral lymphocytosis.2 Thus, macroglobulinemia has variable morphologic manifestations.
IgM consists of five subunits which have the general structure of all immunoglobulins, namely a pair of type specific heavy chains and a pair of light chains of either the κ type or the λ type. Five such subunits combine to form an IgM molecule (μ2 κ2)5 or (μ2 λ2)5. In 20% to 30% of the patients Bence Jones protein is also present.3 Most patients also have traces of uncombined subunits (IgMs), but free μ chains in this disease have not
Bhoopalam N, Lee BM, Yakulis VJ, Heller P. IgM Heavy Chain Fragments in Waldenström's Macroglobulinemia. Arch Intern Med. 1971;128(3):437-440. doi:10.1001/archinte.1971.00310210113013