Significant association between renal function and amyloid-positive area in renal biopsy specimens in AL amyloidosis

Abstract

Background: The kidney is a major target organ for systemic amyloidosis that often affects the kidney including proteinura, and elevated serum creatinine (Cr). The correlation between amount of amyloid deposits and clinical parameters is not known. The aim of this study was to clarify correlation the amyloid area in all renal biopsy specimen and clinical parameters.

Methods: Fifty-eight patients with an established diagnosis of AL amyloidosis participated in the study. All patients showed amyloid deposits in renal biopsies. We retrospectively investigated the correlation between clinical data and amyloid occupied area in whole renal biopsy specimens.

Results: The area occupied by amyloid was less than 10% in 57 of the 58 patients, and was under 2% in 40. For statistical analyses, %amyloid-positive areas were transformed to common logarithmic values (Log10%amyloid). Cr showed significant correlation with Log10%amyloid and estimated glomerular filtration rate (eGFR) showed the significant negative correlation. Patient age, cleatinine clearance (Ccr), blood urea nitorogen, and urinary protein was not significantly correlated with Log10%amyloid. The correlation with other clinical factors such as sex, and serum concentrations of total protein, albumin, immunoglobulins, compliments was evaluated. None of these factors significantly correlated with Log10%amyloid. According to sex- and age- adjusted multiple linear regression analysis, Log10%amyloid had significant positive association with Cr and significant negative association with eGFR.

Conclusion: There is significant association between amyloid-positive area in renal tissue and renal function, especially Cr and eGFR. The level of Cr and eGFR may be a marker of amount of amyloid in renal tissue.

Figure 1

Histogram showing distribution between numbers of patients and %amyloid area.A: Distribution between numbers of patients and %amyloid area. Fifty-seven out of 58 patients of %amyloid area were under 10%. Forty out of 58 patients were under 2%. B: Distribution between numbers of patients and log₁₀%amyloid area. The distribution was similar to normal probability distribution.

Figure 2

Correlation between Log₁₀ %amyloid and variables. A: Correlation between Log₁₀%amyloid and age. B: Correlation between Log₁₀%amyloid and serum creatinine. C: Correlation between Log₁₀%amyloid and creatinine clearance. D: Correlation between Log₁₀%amyloid and blood urea nitrogen. E: Correlation between Log₁₀%amyloid and uric acid. F: Correlation between Log₁₀%amyloid and urinary protein. G: Correlation between Log₁₀%amyloid and eGFR. Patient age was significantly correlated with Log₁₀%amyloid. Cr and eGFR showed significant correlation with Log₁₀%amyloid. Other clinical parameters did not showed significant correlation with Log₁₀%amyloid.