Which finding is seen on serum protein electrophoresis in multiple myeloma?

• A. Polyclonal gammopathy
• B. Decreased IgG levels
• C. No protein spike
• D. Monoclonal (M) protein spike on SPEP

Answer: (D)

The key concept is that multiple myeloma involves a single clone of malignant plasma cells that overproduces one type of immunoglobulin. On serum protein electrophoresis this shows up as a sharp, narrow monoclonal spike—an M protein—in the gamma region (often IgG or IgA, sometimes light chains). This monoclonality distinguishes it from polyclonal increases, which broaden the gamma region rather than producing a discrete spike. Other choices describe patterns that don’t fit myeloma: a diffuse broad increase would be polyclonal gammopathy, decreased IgG suggests immunoglobulin deficiency, and no protein spike would be inconsistent with the presence of the monoclonal protein. Thus the monoclonal (M) protein spike on SPEP is the characteristic finding.