Significant association between renal function and area of amyloid deposition in kidney biopsy specimens in reactive amyloidosis associated with rheumatoid arthritis.

The kidney is a major target organ for systemic amyloidosis, resulting in proteinuria and an elevated serum creatinine level. In patients with reactive amyloidosis associated with rheumatoid arthritis, a correlation between the amount of amyloid deposits and clinical parameters is not known. The purpose of this study was to clarify the association between various factors including renal function and the area of amyloid deposition in these patients. Fifty-eight patients with an established diagnosis of reactive AA amyloidosis were studied. We retrospectively investigated the correlation between clinical data and the area occupied by amyloid in renal biopsy specimens. All the patients showed amyloid deposits in renal tissues, and the percentage of the area occupied by amyloid was <10% in 54 of them. Mesangial proliferative glomerulonephritis and membranous nephropathy were frequently combined with renal amyloidosis. For statistical analyses, the percentage of the area occupied by amyloid was transformed to a common logarithmic value (Log(10) % amyloid), as the histograms showed a log-normal distribution. Log(10) % amyloid was found to be correlated with age, creatinine (Cr) level, creatinine clearance (Ccr), blood urea nitrogen (BUN) level, and the estimated glomerular filtration rate (eGFR). Multiple linear regression analyses were then performed to examine the sex- and age-adjusted association between Log(10) % amyloid and each of the clinical variables. Cr, Ccr, BUN, UA, CRP, and eGFR were significantly correlated with Log(10) % amyloid, but urinary protein was not. There was a significant correlation between the area of amyloid deposition in renal tissue and parameters of renal function, especially Cr and Ccr. If amyloid deposition in renal tissue can be arrested or prevented, then it may be possible to maintain renal function at an acceptable level.