The photomicrograph shows an interstitial granuloma from a case of granulomatous interstitial nephritis. The presence of granulomas within interstitial nephritis frequently raises the differential diagnosis of unusual infections such as fungal and mycobacterial. However, a case series conducted within the United States showed that drug-induced reactions are the etiology of 45% of granulomatous interstitial nephritis cases followed by sarcoidosis in another 30%. The remaining 25% included 10% of cases that were idiopathic and 15% due to a variety of other etiologies such as systemic vasculitis, foreign body giant cell reaction, and infection.

Reference: Bijol V, et al. Int J Surg Pathol 14: 57-63, 2006