Monoclonal bands of IgM on serum immunofixation are most strongly associated with which disease?

• A. Multiple myeloma
• B. Waldenström's macroglobulinemia
• C. Acute leukemia
• D. Cirrhosis

Answer: (B)

Monoclonal IgM bands detected by serum immunofixation point to a single clone of cells producing IgM, which is a hallmark pattern for Waldenström's macroglobulinemia (lymphoplasmacytic lymphoma). In this disorder, malignant B‑cells and plasmacytoid cells secrete an IgM monoclonal protein, creating a characteristic IgM M-protein on immunofixation and often an IgM “spike” on electrophoresis. Clinically, this IgM paraprotein can drive hyperviscosity and related symptoms, making the IgM focus a key diagnostic clue.

In contrast, multiple myeloma most commonly involves monoclonal IgG or IgA, with IgM paraproteins being unusual. Acute leukemia doesn’t typically present with a monoclonal IgM band, and cirrhosis tends to produce polyclonal hypergammaglobulinemia rather than a single monoclonal IgM, so it doesn’t generate the same immunofixation pattern. Thus, the strongest association of monoclonal IgM bands on serum immunofixation is Waldenström's macroglobulinemia.