Clinicopathological Characteristics and Long-Term Kidney Outcomes in Biopsy-Proven Renal Sarcoidosis.

Abstract

Background: Renal sarcoidosis (RS) is a rare but potentially severe manifestation of sarcoidosis, primarily affecting the kidneys through granulomatous interstitial nephritis (GIN) and calcium metabolic disturbances. This study evaluates the clinicopathological features and renal outcomes of biopsy-proven RS, focusing on identifying predictors of renal recovery and disease progression.

Methods: This retrospective study included 43 biopsy-proven RS at Mayo Clinic (2012-2024). Demographic, clinical, laboratory, and histopathological data were analyzed. Renal recovery within six months was classified as complete, partial, or no recovery based on serum creatinine (sCr) changes. Long-term adverse composite outcomes included the chronic kidney disease (CKD) onset, CKD progression, end-stage kidney disease, dialysis initiation, or death. Logistic regression and Cox proportional hazards regression were used to assess predictors of renal outcomes.

Results: Among cohort, 84% exhibited interstitial nephritis, with GIN in 33%. Calcium phosphate deposits were found in 58% of cases. Hypercalciuria (90%) was more common than hypercalcemia (74%). Within six months, 86% achieved recovery (74% complete, 12% partial), while 40% experienced long-term adverse composite outcomes. Higher sCr at biopsy (≥ 2.4 mg/dL) and moderate-to-severe interstitial fibrosis and tubular atrophy (IFTA) were associated with reduced complete recovery and worse long-term outcomes; while pre-existing CKD significantly increased the risk of adverse long-term outcomes. Steroid therapy significantly increased the likelihood of complete recovery and reduced the risk of adverse long-term outcomes.

Conclusions: Pre-existing CKD, elevated sCr at biopsy, IFTA, and steroid therapy are key predictors of renal outcomes in RS. Early diagnosis and intervention are crucial to preventing irreversible kidney damage.