Background: The IgA nephropathy (IgAN) Study Group in Japan conducted a multicenter, randomized, controlled trial of tonsillectomy with steroid pulse therapy (TSP) versus steroid pulse monotherapy in patients with IgAN (UMIN Clinical Trial Registry Number; C000000384). The effects of therapies in relation to pathological severity were analyzed in this study. Methods: The patients with IgAN, urinary protein 1.0–3.5 g/day, serum creatinine of 1.5 mg/dl or less were randomly assigned to receiving TSP (Group A) or steroid pulses alone (Group B). The primary endpoint was the disappearance of proteinuria and/or hematuria. Twenty-six biopsies in Group A and 33 in Group B were available. The histological grades (HG) according to the percentage of glomeruli with crescent or sclerosis and the Oxford classification were analyzed. Results: The patients in Group A had a 4.32- to 12.1-fold greater benefit of disappearance of proteinuria and 3.61- to 8.17-fold greater benefit of clinical remission (disappearance of proteinuria and hematuria) than those in Group B in patients with HG2–3, acute lesions (cellular or fibrocellular crescent) affecting more than 5 % of glomeruli, chronic lesions (fibrous crescents or sclerosis) affecting more than 20 % and S1. In contrast, odds ratios for disappearance of proteinuria or clinical remission in Group A to Group B were not significant in patients with HG 1, acute lesion in 5 % or less of glomeruli, chronic lesion in 20 % or less and S0. The disappearance of hematuria showed no relation to pathological severity. Conclusion: TSP might be better employed according to the pathological severity.
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