An Unusual Etiology of Recurrent Parathyroid Hormone-Independent Hypercalcemia

The diagnosis of parathyroid hormone (PTH)-independent hypercalcemia can be challenging due to its heterogeneous etiology. We report a case of a 65-year-old woman diagnosed with PTH-independent hypercalcemia 7 years prior. In view of elevated serum acetylcholine esterase and 1,25-dihydroxyvitamin D, a granulomatous etiology was suspected. The ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) revealed diffuse uptake in the axial and appendicular muscles, suggestive of sarcoidosis of muscle. She responded to a 6-week course of glucocorticoids, with normalization of calcium levels that was sustained for 7 years until her recent presentation with weight loss and anorexia. The current laboratory parameters mimicked the pattern of the last episode, and the ¹⁸F-FDG PET-CT also showed a similar isotope uptake in axial and appendicular muscles, most prominently in the paraspinal, gluteal, and thigh muscles. No additional FDG-avid lesion was detected on the PET-CT scan. An ultrasound-guided muscle biopsy from the right mid-paraspinal muscle demonstrated a lymphoplasmacytic infiltrate with epithelioid cell granuloma and Langhans giant cells, consistent with sarcoidosis. The hypercalcemia responded promptly to glucocorticoid therapy, which was tapered over 2 months. A final diagnosis of PTH-independent recurrent hypercalcemia due to isolated muscle sarcoidosis was reached, representing an unusually rare manifestation of sarcoidosis.