Severity of nephrotic IgA nephropathy according to the Oxford classification

Abstract

IgA nephropathy with nephrotic syndrome (nephrotic IgAN) is a rare form of IgAN. Its prognosis and response to steroid therapy are still controversial because the differential diagnosis between nephrotic IgAN and minimal change nephrotic syndrome with IgA depositions is sometimes confused. In this retrospective cohort analysis, we accurately diagnosed 42 cases of nephrotic IgAN (4.4%) from 954 IgAN patients, according to the Oxford classification. We analyzed the clinical and histological data, prognosis, and response to steroid therapy. In nephrotic IgAN, mean estimated glomerular filtration rate (eGFR) was 51.1 ± 24.6 ml/min, proteinuria was 5.71 ± 2.56 g/day, and urinary red blood cells were 51.0 ± 37.8 high power field. Both active and chronic histological lesions were observed. Cumulative renal survival rate was significantly lower in nephrotic IgAN than in non-nephrotic IgAN (the control group consisted of 47 non-nephrotic IgAN patients diagnosed between 1995 and 1996) (log-rank test: P < 0.0001). The cases with steroid therapy significantly improved their prognosis, though their male-to-female ratio and blood pressure level measured at renal biopsy were significantly lower than in the cases without steroid therapy. Steroid therapy was particularly effective in cases with low-grade tubular atrophy and interstitial fibrosis (T-grade in Oxford classification). Without steroid therapy, lower eGFR and higher T-grade were independent risk factors for severe outcome by multivariate Cox regression. Nephrotic IgAN is a very severe form of IgAN, with renal dysfunction, massive hematuria, and active and chronic histopathological lesions. Renal outcome is severe; however, steroid therapy can improve prognosis in cases with higher eGFR and lower T-grade, according to the Oxford classification.