American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a defining characteristic for the diagnosis of Waldenström macroglobulinemia?

1. Presence of IgM monoclonal gammopathy in the serum

2. Bone marrow biopsy showing over 20% plasma cells

3. Elevated serum calcium levels

4. Bone marrow demonstrating absence of small lymphocytes

The correct answer is: Presence of IgM monoclonal gammopathy in the serum

The defining characteristic for the diagnosis of Waldenström macroglobulinemia is the presence of IgM monoclonal gammopathy in the serum. This condition is specifically characterized by the overproduction of IgM antibodies due to the proliferation of lymphoplasmacytic cells, which are a mix of lymphocytes and plasma cells. The identification of elevated levels of IgM in the serum is crucial because it not only supports the diagnosis but also helps differentiate Waldenström macroglobulinemia from other plasma cell disorders, such as multiple myeloma, which typically involves a different type of immunoglobulin. The other options, while potentially relevant to the broader context of hematologic disorders, do not serve as definitive characteristics for Waldenström macroglobulinemia. For example, the presence of over 20% plasma cells in a bone marrow biopsy is more indicative of multiple myeloma rather than specifically Waldenström macroglobulinemia. Similarly, elevated serum calcium levels are often associated with multiple myeloma due to bone resorption but are not a distinctive feature of Waldenström macroglobulinemia. Lastly, the statement regarding the absence of small lymphocytes in the bone marrow does not accurately reflect the typical findings in Walden