Epidemiological and clinicopathological characteristics of vascular-limited renal AL amyloidosis

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BACKGROUND: 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, with these vascular-limited forms following a distinct clinical course, but very little is known about these forms. Our work planned to better characterize renal vascular-limited AL amyloidosis. METHODS: By mining a 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. RESULTS: 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 181 (133-216) 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 free light chain 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 was 59 months-significantly longer in patients who achieved a deep hematological response (178 vs 20 months, P = .002). CONCLUSION: 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.

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