| Summary: | Renal involvement is rare in systemic sarcoidosis. Among renal manifestations, tubulointerstitial nephritis (TIN) is the most commonly reported finding. We conducted the current study to investigate the clinical, laboratory, and histological features and to analyze the outcome of TIN due to sarcoidosis. We present a retrospective, single-center study of patients followed for sarcoidosis and presenting with TIN related to this systemic disease. Twenty-four patients were assessed (22 females/2 males). The mean age at diagnosis of TIN was 46.3 years. Extrarenal manifestations were dominated by thoracic involvement (95.8%), peripheral lymph nodes (54.2%), and skin lesions (33.3%). The mean proteinuria level was 0.68 g/24 h. Renal failure was diagnosed in 83.3% of cases with a median estimated glomerular filtration rate at 14.3 mL/min/1.73 m2. Nine patients presented with hypercalcemia and 12 patients with hypercalciuria. Renal biopsy was performed in 58.3% of cases. Six of the 14 patients presented with noncaseating granulomatous interstitial nephritis and eight with interstitial nephritis without granuloma. Granulomatous infiltration of renal parenchyma was complicated by vasculitis in two cases. Corticosteroid therapy was used in all patients. On follow-up analysis, four patients progressed to end-stage renal disease (ESRD) after a mean duration at 45.5 months. In the remaining patients, kidney function statistically significantly improved after one month of treatment compared to the time when the diagnosis was initially established (P = 0.031). We found that the predictive factors of progression to ESRD were multiorgan involvement (P = 0.032), advanced fibrosis F3 (P = 0.0006), and extensive interstitial granulomas (P = 0.007) and these were independently correlated with ESRD. Corticosteroid therapy seems to be effective in sarcoid TIN, but some degree of persistent renal failure is possible which can be predicted from both histologic findings and initial response to steroid therapy.
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