Which condition is indicated by a monoclonal antibody spike in serum?

A monoclonal antibody spike in serum is a hallmark finding in multiple myeloma, a type of hematologic malignancy characterized by the proliferation of a single clone of plasma cells. These abnormal plasma cells produce excess amounts of a specific type of immunoglobulin, leading to what is referred to as a "monoclonal protein" or "M protein." When serum protein electrophoresis is performed, this excess protein manifests as a distinct spike on the graph, indicating elevation in the specific monoclonal immunoglobulin (usually IgG or IgA).

The presence of this spike is significant for diagnosis and monitoring of the disease, as it correlates with disease burden and response to treatment. In contrast, conditions like chronic lymphocytic leukemia (CLL), lymphoma, and myelodysplastic syndromes don't typically feature a monoclonal protein spike, although they may involve other abnormal findings in blood tests or bone marrow analysis. Thus, the presence of a monoclonal antibody spike directly supports the diagnosis of multiple myeloma, underlining its importance in clinical practice.