Silent Lungs, Loud Kidneys: Renal Sarcoidosis

Introduction: Renal sarcoidosis is rare, often occurring with extrarenal disease. Its true incidence is unknown, though autopsies reveal granulomatous interstitial nephritis in up to 23% of sarcoidosis cases. We report a case of biopsy-proven renal sarcoidosis in a patient with stable lung imaging but declining renal function. Case Description: 71 yo woman with stable mediastinal lymphadenopathy and weight loss was referred for AKI (Cr 0.8→1.8mg/dL over 8 months). Workup showed mild proteinuria, hypercalcemia, anemia, elevated 1,25-vit D, and inflammatory markers. Without pulmonary progression to justify treatment, she underwent a renal biopsy, which revealed granulomatous tubulointerstitial nephritis and nephrocalcinosis, consistent with sarcoidosis. She was started on prednisone 40mg daily with improved Cr to 1.0 at 12 wks, and normalization of calcium levels, hemoglobin, and CRP. Discussion: Renal sarcoidosis is rare, especially without other organ involvement. As such, requiring a kidney biopsy to change management is uncommon. Classic findings include granulomatous interstitial nephritis, but non-granulomatous interstitial nephritis and nephrocalcinosis can also occur. Biopsy can aid with prognosis, as the extent of fibrosis may predict steroid response. Early treatment with steroids (0.5-1mg/kg/day) is key to preventing ESKD, but no formal guidelines exist. Our patient responded to an initial dose of 0.7mg/kg prednisone, with renal function improving near baseline in 12 weeks. However, with relapse rates of 30-40%, long-term management remains a challenge needing further research.