Gilbert Moeckel, MD, PhD, FASN

Granulomatous interstitial nephritis (GIN) is a rare histologic diagnosis characterized by epithelioid renal interstitial granulomas. It is reported in less than 1% of native renal biopsies and 0.6% of renal transplant biopsies. Men and women are affected equally, usually within the sixth decade of life. Underlying causes of GIN include drug reaction, infection, sarcoidosis, Granulomatosis with Polyangitis (GPA), and crystal deposition. Unclassifiable cases are by default considered idiopathic. Drug reactions and sarcoidosis are the most common causes in the western world, while infectious etiologies, such as tuberculosis, may be responsible for the majority of cases in endemic regions. In renal transplant grafts, fungi and mycobacteria are the main causes. Clinically, a variable degree of renal failure and mild proteinuria are characteristic , while microscopic hematuria and leukocyturia are less common features. Treatment consists of anti-inflammatory drugs for several months, however, long term renal replacement therapy has been necessary in some cases. Histologically, the distinction between the various etiologies of GIN is challenging. While diagnostically useful differences exist, there is a paucity of literature addressing these features.