Renal sarcoidosis with normal serum vitamin D and refractory hypercalcemia
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Sarcoidosis is a multi-system disorder characterized by non-caseating epithelioid granulomas in multiple organs. Renal involvement may usually occur as granulomatous interstitial nephritis, but renal failure is uncommon. We report a case of renal-limited sarcoidosis diagnosed by renal biopsy, associated with abnormal calcium metabolism.
A 30-year-old Caucasian male presented with unexplained renal function impairment and hypercalcemia. The patient did not have any history of kidney disease, cough, skin rash, dysuria, hematuria or any other symptoms. Physical examination was unremarkable. Serum creatinine was 2.2 mg/dl and serum calcium was 11.5 mg/dl. Serum intact parathyroid hormone level (12 pg/mL) was decreased. Serum angiotensin-converting enzyme (ACE), 1,25-dihydroxyvitamin D (1,alpha-25 vit D) and pre-proparathyroid hormone (PTHrP) levels and urinary calcium excretion were all in normal range. The renal biopsy showed severe interstitial nephritis with non-caseating granuloma. The patient was treated with prednisone with starting dose of 1 mg/kg. After 2 months of prednisone therapy, serum creatinine decreased. However, because of continued of hypercalcemia unresponsive to low calcium diet and prednisone, chloroquine was prescribed. Six months after the onset, the patient's serum creatinine is stable at 1.30 mg/dl, serum calcium is 10.8 mg/dl, and serum ACE and 1,alpha-25 vit D levels are in normal range. He does not have any signs of extra-renal relapse.
The mechanisms of abnormal calcium metabolism in this patient with renal-limited sarcoidosis are unclear.