Background: Renal failure in sarcoidosis is rare and data on its long-term outcome are scarce. Aim: To investigate the pattern of renal involvement in sarcoidosis, its clinical course and response to treatment in the long-term. Methods: A single-center retrospective study with review of renal biopsies and medical charts was performed. Results: Between January 2005 and December 2016, seven patients with sarcoidosis underwent a kidney biopsy. This is equivalent to a frequency of 1.6% in a total of 434 biopsies from native kidney performed in our institution. All patients presented with renal failure. Five patients had granulomatous interstitial nephritis (GIN) and one patient each interstitial nephritis without granuloma and nephrocalcinosis. Three patients had concomitant glomerular disease: IgA nephropathy (n = 2), membranous and focal proliferative glomerulonephritis (n = 1). Most patients (n = 5) presented with hypercalcemia. All patients initially received oral prednisolone 1 mg/kg/day (n = 3) or 0.5 mg/kg/day (n = 4), respectively, with subsequent tapering or suspension. One patient was started on azathioprine after 18 months to spare steroids. After a mean follow-up of 59 months mean estimated glomerular filtration rate (eGFR) had improved from 19 ± 7 at presentation to 49 ± 16 mL/min. No patient required dialysis. All patients started on prednisolone 1 mg/kg/day developed transient diabetes mellitus while patients on 0.5 mg/kg/day did not. Renal function improvement did not differ between both treatment groups. Conclusion: GIN was the most common diagnosis in sarcoidosis patients with renal failure. Initial hypercalcemia was observed in the majority. Early steroid treatment lead to sustained renal function improvement.

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Granulomatous interstitial nephritis is a rare finding in renal biopsy caused by drugs, infections, and inflammatory or autoimmune diseases. Idiopathic cases account for 18% of granulomatous interstitial nephritis in native kidneys. Sarcoidosis and drugs are the most common causes of granulomatous interstitial nephritis in Western countries, while in India tuberculosis prevails. Few cases of renal sarcoidosis without extrarenal involvement, that is, isolated renal sarcoidosis, have been reported. The diagnostic criteria of isolated renal sarcoidosis remain, however, unclear. Extrarenal sarcoidosis and other etiologies of granulomatous interstitial nephritis, in particular drug-related, have to be excluded. Some of these patients may develop extrarenal manifestations during follow-up. Changes in calcium and vitamin D metabolism are frequently observed in renal sarcoidosis and support its diagnosis. While non-necrotizing granulomas are a feature of sarcoidosis and drug-induced granulomatous interstitial nephritis, they also prevail in tuberculosis-associated granulomatous interstitial nephritis. Granulomatous interstitial nephritis caused by sarcoidosis and drugs usually responds to steroid therapy. A poor response to steroids may indicate an infectious etiology such as tuberculosis and should lead to a review of the initial diagnosis. This article gives an overview of the various etiologies of granulomatous interstitial nephritis, their frequency and histopathological characteristics, as well as potential biomarkers associated with renal sarcoidosis.