Clinicopathological Characteristics and Prognostic Implications of Periodic Acid-Schiff-Positive Amyloid Deposits in Renal AL Amyloidosis

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Introduction: It has been recognized that periodic acid-Schiff (PAS) staining of amyloid deposits is typically weak or negative in the majority of AL amyloidosis. However, a subset of patients exhibits PAS-positive deposits, and their clinicopathological significance remains unclear. Methods: We retrospectively analyzed 269 patients with renal biopsy-proven AL amyloidosis from our institution; 72 were classified as PAS positive and 197 as PAS negative. Baseline demographics, clinical data, renal pathology features, treatment strategies, and prognostic information were collected. Multivariable linear regression and Cox proportional hazards models were used to determine the impact of PAS-positive amyloid deposition on renal function and patients’ outcomes. Results: Compared with the PAS-negative group, PAS-positive patients had higher serum creatinine (94.40 vs. 79 μmol/L, p = 0.005) and increased renal insufficiency ratio (31.94% vs. 14.72%, p = 0.002). Histopathology showed more severe glomerular and interstitial amyloid deposition (p = 0.037, p = 0.049, respectively). In multivariable linear regression, PAS-positive deposits (β = 0.158, p = 0.005) were independently associated with higher serum creatinine. PAS-positive patients showed significantly worse renal survival (HR: 3.05, 95% CI: 1.40–6.65, p = 0.005), independent of age, treatment regimens, renal stage, and pathological cores. Meanwhile, PAS-positive staining was an adverse prognostic factor (HR: 2.34, 95% CI: 1.24–4.43, p = 0.009) for overall survival after adjusting for AL type, age, treatment, organ involvement, interstitial fibrosis and tubular atrophy, and total amyloid burden. Conclusion: PAS-positive amyloid deposits are associated with more severe renal injury and poorer prognosis in AL amyloidosis.

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