Sarcoidosis Presenting with Isolated Kidney Involvement: A Case of Granulomatous Interstitial Nephritis

Introduction: Sarcoidosis is a multisystem granulomatous disease of unclear etiology, most commonly affecting the lungs and lymphatic system. Renal involvement, though less frequent, can manifest with electrolyte disturbances or overt kidney injury. A key mechanism of renal dysfunction is dysregulated calcium metabolism due to extrarenal 1,25-dihydroxyvitamin D production by activated macrophages. Here, we present a case of sarcoidosis, initially manifesting as hypercalcemia and acute kidney injury (AKI). Case Description: A 50-year-old male with no past medical history was referred to ED after labs showed hypercalcemia (14.5 mg/dL) and elevated creatinine (3.84 mg/dL; baseline 1.9 mg/dL a year prior). He recently started vitamin D (5000 IU), K2, and magnesium supplements for deficiency. He also reported prior blurry vision in the left eye, treated empirically with steroid eye drops, with symptom resolution. He denied systemic symptoms. Hospital evaluation revealed suppressed PTH (7), elevated ACE (161), PTHrP (3.2), and 1,25 DOH (201.3). CT chest showed diffuse pulmonary nodules with mediastinal and retroperitoneal lymphadenopathy. Urinalysis and paraproteinemia workup were unremarkable. He was treated with IV fluids, calcitonin, and denosumab, correcting hypercalcemia, but AKI persisted. Kidney biopsy showed noncaseating granulomatous interstitial nephritis, acute tubular injury, 65% interstitial fibrosis, and 40% tubular atrophy; stains for AFB and fungi were negative. Findings were consistent with renal sarcoidosis. Discussion: Renal sarcoidosis is an underrecognized extrapulmonary manifestation, seen in up to 22% of systemic cases. It often presents as GIN and can cause kidney dysfunction if not identified early. In this case, sarcoidosis manifested as AKI and hypercalcemia, without pulmonary symptoms. Prior ocular symptoms were likely granulomatous uveitis—an early clue. Dysregulated 1,25 (OH) D production by granulomatous macrophages increases calcium absorption and causes renal injury. High-dose vitamin D may have unmasked his subclinical disease. While corticosteroids are first-line, chronic injury on biopsy can limit recovery. Sarcoidosis should be considered in unexplained hypercalcemia with renal dysfunction, even without pulmonary signs, as early diagnosis and care are key to preventing irreversible damage.