A Modern Primer on Light Chain Amyloidosis in 592 Patients With Mass Spectrometry-Verified Typing

Objective: To describe the clinical and laboratory characteristics of patients with meticulously typed light chain (AL) amyloidosis.

Patients And Methods: Patients (N=592) with biopsy-proven, mass spectrometry-confirmed AL amyloidosis diagnosed from January 1, 2008, through August 31, 2015, were included.

Results: The median patient age at diagnosis was 63 years. Thirty-four percent of patients (n=204) had isolated organ involvement, mostly heart (19% [n=115]) followed by kidney (9% [n=53]). In contrast, 25% (n=146) had more than 2 involved organs. Patients with isolated cardiac involvement had similar cardiac dysfunction compared with those with nonisolated cardiac amyloidosis. In contrast, isolated renal involvement was associated with increased proteinuria and higher estimated glomerular filtration rate compared with nonisolated renal amyloidosis. Serum and urine immunofixation electrophoresis results were positive in 80% and 88% of patients, respectively, with 94% of patients having at least 1 positive immunofixation electrophoresis result (serum or urine). The serum free light chain ratio was abnormal in 91% of patients. When all monoclonal protein studies were combined, only 1 patient (0.2%) had normal results. The 1- and 5-year survival rates were 65% and 46%, respectively. Survival of patients with cardiac amyloidosis was not influenced by the number of involved organs (1 vs >1 organ), emphasizing the prognostic significance of cardiac involvement.

Conclusion: When mass spectrometry is used to definitively type amyloid, only a fraction of a percent of patients with AL have negative monoclonal protein studies, unlike historical reports. Patient characteristics and outcomes of accurately typed patients are described.