Parathyroid-independent hypercalcemia as initial presentation of renal sarcoidosis with granulomatous interstitial nephritis: a case report.

Background: Sarcoidosis is a multisystem granulomatous disorder predominantly affecting the lungs. Renal sarcoidosis often presents diagnostic challenges, PTH-independent hypercalcemia may be a clinical feature. Case Report: A 48-year-old Asian female presented with persistent hypercalcemia (2.81 mmol/L), suppressed Parathyroid hormone PTH(1.24 pg/mL), and renal dysfunction (serum creatinine 2.02 mg/dL). Initial imaging showed mediastinal lymphadenopathy, 1.biopsy could not be performed as the size and location of the lymph nodes precluded safe conduct of the procedure, but bone marrow puncture and PET/CT excluded malignancy. A renal biopsy performed three months later demonstrated focal multinucleated giant cells and calcium deposits-confirming renal sarcoidosis. She was initiated on methylprednisolone (16 mg/day), leading to normalized calcium levels and improved renal function (serum creatinine stabilized at 1.1 mg/dL). However, despite strictly following the treatment plan, she still underwent ureteroscopy lithotripsy due to recurrent episodes of nephrolithiasis. Long-term follow-up after drug discontinuation showed that the patient's calcium and PTH levels remained normal, while there was a mild impairment in renal function. Discussion: This case underscores the diagnostic difficulty of renal sarcoidosis, particularly in hypercalcemic patients without renal biopsy. Early use of corticosteroids can improve renal function, but complications like nephrolithiasis may still occur, so continuous monitoring is still necessary. A high index of suspicion and timely biopsy are essential for diagnosis and optimal management.