Acute Interstitial Nephritis and Nephrotic Syndrome in a Patient with Controlled HIV: A Case of Syphilis-Related Nephropathy

Introduction: Syphilis-related nephropathy is an uncommon but important cause of renal dysfunction and proteinuria. While HIV-associated nephropathy (HIVAN) and immune complex-mediated diseases are well documented, syphilis should remain on the differential diagnosis in patients with unexplained kidney injury and positive serologies. Case Description: 38-year-old man with controlled HIV on ART, presented with 2 weeks of progressive lower extremity edema, an 8-pound weight gain, and elevated systolic blood pressures to the 180/120 mm/Hg. Initial evaluation revealed significant proteinuria, a serum creatinine of 2.5 mg/dL, and a UPCR of 9.86 g/g. Serum albumin was 2.3 g/dL. A kidney biopsy demonstrated acute interstitial nephritis (AIN) with eosinophilic infiltrates and acute tubular injury with diffuse foot process effacement consistent with nephrotic syndrome and acute interstitial nephritis. There were no immune complex deposits tubuloreticular inclusions, or histologic features suggestive of HIVAN or HIVICK. The patient was not taking any medications commonly associated with AIN. Further workup revealed a positive rapid plasma reagin (RPR) of 1:32, he was treated with penicillin. In the absence of other identifiable causes, syphilis was considered the most likely etiology. The patient was started on an angiotensin receptor blocker for proteinuria and blood pressure management. Patient remained off immunosuppressive therapy, follow-up labs showed a stabilized creatinine and improvement in UPCR to 7.2 g/g. Discussion: This case highlights syphilis as a rare but important cause of nephrotic syndrome and AIN in an HIV-positive patient. Although membranous nephropathy is the more commonly reported histologic pattern, this patient’s biopsy demonstrated diffuse podocyte injury and interstitial inflammation without immune deposits. In the absence of alternative causes and a positive RPR, an etiology of syphilis related proteinuria and AIN should be considered. Early recognition and early treatment with antimicrobials may avoid the use of unnecessary immunosuppression, leading to recovery of renal function. Chronic histologic changes, however, may limit the degree of renal improvement in this patient. This case emphasizes the importance of a thorough infectious workup and biopsy in guiding management and in avoiding unnecessary immunosuppression.