Incidence and Prevalence of Light Chain Amyloidosis: A Population-Based Study

Background: Systemic light chain (AL) amyloidosis is considered a rare disease, but knowledge of its exact incidence and prevalence is based on old data involving limited populations.

Aim: To determine the incidence and prevalence of AL amyloidosis in the general population.

Patients and Methods: The national reference center for AL amyloidosis is located in the CHU de Limoges in Limoges (France), the administrative center of the Limousin region (738,110 inhabitants in 2014). A comprehensive and exhaustive database of AL amyloidosis patients diagnosed in this region has been computerized since January 2007. All patients living in the Limousin region and with a first diagnosis of systemic AL amyloidosis between January 1, 2012, and December 31, 2016, were retrospectively included to determine the disease incidence. All departments and laboratories of pathology were contacted in the region, and any possible missing cases diagnosed during the same period were collected. Prevalence was determined as all living patients with AL amyloidosis during 2016 regardless of the diagnosis date. Cardiac involvement was defined according to current definition (ie, mean wall thickness >12 mm in the absence of other causes of left ventricular hypertrophy). Renal involvement was defined as proteinuria >0.5 g/L (predominantly albumin) in the absence of other etiology.

Results: Over the 5-year period, 46 new patients in the Limousin region had a confirmed diagnosis of AL amyloidosis (70% men; median age, 72.5 years), corresponding to a crude yearly incidence of 12.5 (95% CI, 5.6-19.4) cases per million inhabitants. The calculated prevalence of AL amyloidosis was 58 (95% CI, 43-73) cases per million inhabitants. Cardiac and renal involvement was found in 70% and 72% of cases, respectively. Mayo Clinic stages I, II, IIIA (NT-proBNP ≤8500 ng/L), and IIIB (NT-proBNP >8500 ng/L) based on cardiac biomarkers were found in 21%, 29%, 29%, and 21% of patients respectively. The underlying disease was multiple myeloma in 19 patients (41%), including smoldering myeloma in 14 patients, MGUS (monoclonal gammopathy of undetermined significance) in 22 patients (48%), IgM in 2 patients, Waldenström disease in 1 patient, low-grade lymphoma in 3 patients, plasmocytoma in 1 patient, and unknown in 1 patient. In this 5 year-period, 16 patients (35%) died.

Conclusion: This is the firstreport of contemporary incidence and prevalence of systemic AL amyloidosis in France. Incidence was slightly higher than the incidence (adjusted to sex and age) previously reported by Kyle et al (Blood, 1992;7:1817-1822), probably corresponding to the progress in the past 20 years in diagnosing this rare disease.