Renal Sarcoidosis: One Disease, Different Kidney Involvements

Abstract

Renal sarcoidosis has a low frequency, from 0.1% to 0.2%, considering American monocentric cohorts of about 10,000 native kidney biopsies performed in 10-year period. Acute kidney injury (AKI), occurring in <1% of patients, brings sarcoidosis to nephrologist’s attention. AKI in sarcoidosis is mainly due to hypercalcemia and sarcoid granulomatous interstitial nephritis (sGIN), the hallmark pathological finding of the disease. AKI related to hypercalcemia generally responds to steroids. At the contrary, not always all sGIN-AKI has a benign prognosis. This chapter will describe the widest casistics of renal sarcoidosis, considering the predictive value of clinical features, laboratory, radiological parameters, and histological patterns regarding induction therapy response to AKI. Rarely sarcoidosis is life-threatening: fatal events could occur during AKI or during the progression from chronic kidney disease (CKD) to end-stage renal disease (ESRD), a high-risk condition for cardiovascular, infectious, and oncological events. AKI to CKD transition due to specific injury of renal sarcoidosis is one of the most interesting aspects for nephrologists, as the reason why only a minority of sGIN cases will develop AKI: generally, sGIN is s a silent finding observed at autopsy in 7–23% of sarcoidosis patients.