Clinical and histological characteristics of renal AA amyloidosis: a retrospective study of 68 cases with a special interest to amyloid-associated inflammatory response.

We retrospectively reviewed the clinicopathological features of a series of 68 renal AA amyloidosis observations collected between 1990 and 2005. The amyloidogenic disease was a chronic infection (40.8%), a chronic inflammation (38%), a tumor (9.9%), a hereditary disease (9.9%), or was undetermined in 1.4% of cases. Nephrotic syndrome and renal insufficiency were noted in 63.1% and 75% of patients, respectively. The distribution pattern of glomerular amyloid deposits was mesangial segmental (14.7%), mesangial nodular (26.5%), mesangiocapillary (32.3%), and hilar (26.5%). Glomerular form was observed in 80.9% of cases and vascular form in 19.1%. AA amyloidosis-related inflammation was noted in 30 patients (44.1%) and appeared as a multinucleated giant cell reaction (27.9%) or a glomerular inflammatory infiltrate (25%), including glomerular crescents (17.6%). At the end of follow-up, 26 patients (38.2%) showed end-stage renal disease. The clinical presentation of glomerular and vascular forms was distinct with a clear predominance of proteinuria in glomerular form. Inflammatory reaction was preferentially observed in biopsies with a codeposition of immunoglobulin chains and/or complement factors in AA amyloid deposits. The distribution pattern of glomerular amyloid deposits and glomerular inflammatory reaction were independent factors influencing proteinuria level. Tubular atrophy, abundance, and distribution pattern of glomerular amyloid deposits at the time of biopsy were independent predictors of renal outcome. In conclusion, the glomerular involvement appeared as the determining histological factor for clinical manifestations and outcome of renal AA amyloidosis. AA amyloidosis-related inflammation could partly result from an immune response directed against AA fibrils and could induce amyloid resolution and crescents.