Lymphoplasmacytic lymphoma (LPL) is a morphologically defined small lymphocytic process that, unlike most of the other entities discussed in the differential diagnosis of CLL, presents a more compelling diagnostic dilemma morphologically than immunophenotypically. As with many small lymphocytic processes, there is a lack of a clear definition and thus a resultant lack of reproducibility in the diagnosis of this so-called entity. Typically, LPLs are CD5-, CD10-, CD23-, CDllc- and may show variable CD20 and sIg depending on the degree of plasma cell differentiation. LPLs may occasionally demonstrate CD5+, raising the possibility of CLL and (when expressing bright sIg and no CD23) creating diagnostic difficulties with other processes such as MCL.
1.7.2. Other Features That Aid in Distinguishing LPL From CLL
Morphologically, the cells in LPL have a lymphoplasmacytoid morphology, and a plasma cell component is usually present, although this component may be absent or less apparent in the peripheral blood. Clinically, patients usually demonstrate a high serum monoclonal IgM (>10 g), often accompanied by hyperviscosity syndrome.
1.7.3. ^ Heavy Chain Disease
^ heavy chain disease is a variant of LPL in which the patient may demonstrate small lymphocytes that are similar in morphology to CLL. The plasma cells in these cases are often vacuolated. Immunophenotypically, however, the lymphocytes are quite distinctive from CLL in that they are CD5- and sIg light chain- but ^ positive (31).
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