A retrospective multicenter cohort study of patients with sarcoidosis and renal involvement.

BACKGROUND: Sarcoidosis is a multisystem granulomatous disease that can involve the kidneys. Renal involvement is often asymptomatic and underdiagnosed, yet timely recognition and treatment are crucial to prevent irreversible kidney damage. Despite its importance, there is a lack of established treatment guidelines for renal sarcoidosis. METHODS: We conducted a retrospective multicenter study across six Dutch hospitals, including patients with biopsy-proven renal sarcoidosis diagnosed between 2010 and 2024. Clinical, laboratory, histopathological, treatment, and outcome data were collected from electronic medical records. Descriptive statistics were used to summarize findings. RESULTS: Twenty-nine patients with biopsy-proven renal sarcoidosis were included (median age 56 years; 66% male). Lung involvement was present in 48%, and hypercalcemia in 45% of patients. At diagnosis, median serum creatinine was 242 µmol/L and median eGFR was 23 mL/min/1.73 m². Granulomatous inflammation was present in 76% of biopsies. All patients received corticosteroids as first-line therapy (median initial prednisone dose 0.66 mg/kg/day). Maximal improvement in kidney function was observed within one month of treatment; no significant predictors for early response were identified. Relapses occurred in 48% of patients (median time to first relapse: 7 months), often during or after tapering of corticosteroids. Additional immunosuppressive agents were used in 45% of patients, mainly after relapse. No baseline factors predicted relapse risk. CONCLUSIONS: This study confirms the heterogeneous presentation of sarcoidosis and underscores the need for better biomarkers to guide treatment and decision making in these patients. Early corticosteroid therapy leads to rapid improvement in kidney function, but relapse is common during tapering. Steroid-sparing agents are effective for relapsing disease. Close monitoring during and after corticosteroid tapering is warranted. Our findings support a treatment protocol starting with prednisone 0.5–1 mg/kg/day, followed by gradual tapering, and the addition of steroid-sparing agents in case of relapse. Further prospective studies are needed to optimize treatment strategies and identify predictive markers for relapse and response. CLINICAL TRIAL NUMBER: Not applicable.