Isolated Renal Sarcoidosis: a Rare Cause for Granulomatous Interstitial Nephritis

Introduction: Granulomatous interstitial nephritis (GIN) is a rare histological diagnosis that can be the first manifestation of systemic disease. It has been associated with medications, infections, sarcoidosis, crystal deposits, paraproteinemia and Wegnere's granulomatosis. It can also be seen in an idiopathic form. Case report: A 37 year-old female patient presented to our nephrology service with lethargy and weight loss of three months duration. Her past medical history and clinical examination were not remarkable. She had impaired renal function tests and hypercalcemia associated with elevated angiotensin converting enzyme levels and sonographically normal kidneys. Extensive investigations revealed no other organ involvement and no evidence of infection or malignancy. Renal biopsy showed extensive interstitial non-necrotizing granulomata. Accordingly, she was diagnosed as a case of isolated renal sarcoidosis and started on steroid therapy. Within one month of treatment, she recovered normal renal function. Steroids were successfully tapered after another six months, and she shows no evidence of recurrence 24 months after steroid withdrawal. Conclusion: The possibility of isolated renal sarcoidosis should be considered in any case of impaired kidney function and hypercalcemia even in the absence of systemic manifestation. The finding of non-caseating interstitial granulomata in renal biopsy supports this diagnosis. Keywords: granulomatous interstitial nephritis, non-caseating granuloma, renal insufficiency, renal sarcoidosis.