Revisiting medullary tophi: a link between uric acid and progressive chronic kidney disease?

Background: It is well-established from autopsy studies that gouty tophi can form in the kidney, particularly in the renal medulla. Recently hyperuricemia has been identified as a risk factor for progression of chronic kidney disease (CKD). Because each collecting duct serves more than 2,000 nephrons, we postulated that obstruction or disruption of collecting ducts by medullary tophi may explain, at least in part, the association between hyperuricemia and progressive CKD. This work was done to determine the prevalence of medullary tophi in CKD patients. Methods: We queried our nephropathology database over the last 10 years for native kidney biopsies that had medullary tophi. The presence or absence of CKD and uric acid levels around the time of biopsy were determined by chart review. Results: Predominant medullary tissue was reported in 796 of 7,409 total biopsies, and 572 of these were from patients with established CKD. Medullary tophi were seen in 36 patients, 35 of whom had CKD, suggesting a minimum prevalence of tophi in CKD and no-CKD of 6.11 and 0.45%, respectively. Medullary tophi occurred with and without hyperuricemia or a history of gout. Conclusion: Medullary tophi appear to be far more likely to occur in CKD compared to no-CKD patients. This cross-sectional study cannot determine whether medullary tophi are a cause or consequence of CKD. However, given their location and bulk, it is possible that medullary tophi contribute to progression of established CKD by causing upstream nephron damage.