Which statement about monoclonality in amyloid typing is NOT correct?

• A. Monoclonality is suggested by predominance of one light chain on IHC or serum free light chain analysis
• B. Kappa and lambda light chains are involved in amyloid deposition
• C. Monoclonality can be detected by serum free light chain analysis
• D. Monoclonality can be established solely by finding equal amounts of kappa and lambda light chains

Answer: (D)

Monoclonality in amyloid typing hinges on evidence that the amyloid fibrils come from a single clone producing one light chain type, typically indicated by restriction to either kappa or lambda light chains. When immunohistochemistry shows predominance of one light chain, or when serum free light chain analysis reveals an abnormal kappa to lambda ratio, this supports a clonal source for the amyloid. Across cases, either light chain can be involved in deposition, so the presence of kappa or lambda alone does not distinguish the clone—what matters is that one light chain is clearly dominant, pointing to monoclonality. Serum free light chain testing is a useful, minimally invasive way to detect this clonal pattern. However, monoclonality cannot be established solely by finding equal amounts of kappa and lambda light chains; equal levels suggest polyclonal activity or a non-clonal state, and do not indicate a single clonal source.