Epidemiological and clinicopathological characteristics of vascular-limited renal AL amyloidosis

Kidney involvement, along with cardiac disease, is the most frequent manifestation of systemic AL amyloidosis usually resulting in nephrotic-range proteinuria. Rarely, deposits predominantly or exclusively affect the intrarenal arterioles or arteries, these vascular-limited forms following a distinct clinical course, but very little is known about these forms. Our work plan at better characterizing renal vascular limited AL amyloidosis. By mining French Paris hospital database, we found that this unusual phenotype accounts for approximatively 9% of renal AL amyloidosis cases. We retrospectively studied 35 patients with the renal vascular-limited variant of AL amyloidosis on kidney biopsy. All showed predominant or only (n = 21) intra-renal vascular deposits, of lambda isotype in 63%. At diagnosis, median urine protein/creatinine ratio was 0.5 g/g, with serum creatinine of 167 (127-213) µmol/L and estimated glomerular filtration (eGFR) rate of 36.2 (24.3-49.6) ml/min/1,73 m2. Cardiac involvement was present in 67% of cases. A serum and/or urine monoclonal gammopathy was identified in all but one patient and 31 (88%) had an abnormal FLC ratio. Among 28 treated patients, hematological and renal response rates were 75% (including deep hematological response in 43%) and 18%, respectively. Median time from diagnosis to renal event, defined be a composite criterion composed of end-stage renal disease or > 40% decrease in eGFR, was 56 months. Median overall survival (OS) was 59 months, significantly longer in patients who achieved a deep hematological response (178 vs 20 months, p = 0.002). renal vascular limited AL amyloidosis is a probably underdiagnosed disease with markedly reduced eGFR, low-grade proteinuria and severe overall prognosis. Rapid achievement of a deep hematological response is required to preserve long-term renal and patient outcomes.