Calciprotein particles and fibroblast growth factor 23 contribute to the pathophysiology of hypercalcemia in a patient with renal sarcoidosis

In patients with sarcoidosis, dysregulated calcium metabolism is one of the frequently observed complications. However, little attention has been paid to abnormal phosphate metabolism. Herein we present the case of a 42-year-old Japanese man with renal sarcoidosis who developed acute kidney injury due to hypercalcemia and nephrolithiasis. Laboratory data showed hypercalcemia with a normal serum phosphate level and high serum 1,25-hydroxyvitamin D₃, fibroblast growth factor 23 (FGF23) and calciprotein particle (CPP) levels. After treatment with oral prednisone and bisphosphonate, the laboratory abnormalities and renal dysfunction were resolved. Thus increases in FGF23 and CPP may indicate disturbed phosphate metabolism in renal sarcoidosis.