Prevalence of Monoclonal Gammopathy in Wild-Type Transthyretin Amyloidosis

Abstract

ObjectiveTo evaluate the prevalence of monoclonal gammopathy (MG) in patients with wild-type transthyretin amyloidosis (ATTRwt) (formerly known as senile amyloidosis). Patients and MethodsWe retrospectively analyzed the serum protein electrophoresis and serum immunofixation results, free light chain (FLC) levels, and renal function of 113 consecutive patients with ATTRwt seen at the Brigham and Women's Hospital's Cardiac Amyloidosis Program between February 21, 2006, and November 9, 2016. Monoclonal gammopathy was defined as a monoclonal protein present in the serum. Light chain MG was defined as an abnormal serum FLC κ/λ ratio with an elevated FLC level in the absence of a monoclonal protein. In patients with renal dysfunction, the renal FLC reference range was used. ResultsThe mean age of the population was 75 years, 3 of the 113 patients (3%) were female, and 110 (97%) were white. Monoclonal gammopathy was present in 26 patients (23%), 24 of whom had monoclonal protein present and 2 others who met criteria for light chain MG. Most clones (12 of 20 [60%]) were λ restricted. Another 7 patients had an abnormal FLC κ/λ ratio in the setting of renal dysfunction. ConclusionIn this study, MG was present in 23% of patients with ATTRwt. The finding of MG or an abnormal FLC κ/λ ratio in an elderly man may cause diagnostic confusion during subtyping of amyloidosis. A high degree of clinical suspicion for ATTRwt and precise tissue typing using mass spectrometry may overcome such diagnostic challenges.