Renal Interstitial Granuloma as an Adverse Effect of Antibiotics

Introduction: Interstitial granuloma is a rare finding on renal biopsy, opening a wide differential. Etiologies include infectious, autoimmune, drug-induced and idiopathic causes. We present a case of renal granulomatosis identified as a complication of prolonged bacterial pneumonia requiring treatment with several antibiotics. Case Description: A 52-year-old F with history of non-insulin dependent diabetes is admitted following a renal biopsy. In the preceeding months, she was treated for prolonged pneumonia, requiring 2 lines of outpatient oral antibiotics (azithromycin and amoxicillin-clavulanate), and then admission for IV antibiotics. Administration of piperacillin-tazobactam resulted in a full-body rash. Reported serum Cr baseline was 0.5mg/dL, however over a 4-month period from initial respiratory symptoms until biopsy, serum Cr increased to 2.6mg/dL. UA revealed mild proteinuria, pyuria, and hematuria. Urine protein:creatinine ratio was 0.56g. Serologic workup notable for ANA 1:640, negative dsDNA, and a weakly positive anti-histone antibody. Light microscopy revealed non-caseating granuloma with significant interstitial inflammation, and no evidence of vascular or glomerular involvement. Chest imaging was not consistent with pulmonary sarcoidosis and ACE and CH50 were negative. Sputum (x3) and tissue for AFB was negative. She was started on IV and then oral steroids. Cr peaked at 4.40mg/dL. She was discharged on a long prednisone taper. Cr decreasing to 1.5mg/dL, 6 months post steroid initiation Discussion: Renal granulomas can be divided into two categories: caseating and non-caseating. Caseating granulomas raise concern for infection (e.g. mycobacterial) and renal-pulmonary vasculitis syndromes such as EGPA. As for non-caseating granulomas, one must consider the same differential as in acute interstitial nephritis. Antibiotic exposure makes up a large percentage of these cases. This patient had exposure to many antibiotics including a systemic hypersensitivity reaction to one. Other known etiologies of non-caseating granulomas include IBD, sarcoidosis, and tubulointerstitial nephritis and uveitis (TINU) syndrome. This patient was treated with high-dose steroids with a prolonged taper for presumed antibiotic-associated acute interstitial nephritis and creatinine has largely improved.