Multimodality imaging localization of a giant functional parathyroid adenoma in a young fitness trainer with delayed recognition of hypercalcemia: A case report

Giant parathyroid adenoma (GPA) is a rare cause of primary hyperparathyroidism (PHPT) whose symptoms overlap with normal training fatigue and dietary shifts that calcium testing gets delayed in active people. A 36-year-old male fitness trainer presented with 13 kg of unintentional weight loss over six months with weakness, and nocturia, all of which he and the physicians who first saw him attributed to his training regimen and protein supplementation. Serum calcium was 16.4 mg/dL and parathyroid hormone (PTH) 1127.4 pg/mL, with acute kidney injury and bilateral nephrolithiasis; protein electrophoresis and free light chains excluded a paraproteinemic cause. Ultrasonography, 18 F-FDG PET-CT, and Technetium-99m sestamibi scintigraphy were concordant, identifying a right-sided parathyroid adenoma of approximately 2.3 × 2.3 × 5.9 cm extending into the upper mediastinum. Focused right parathyroidectomy was performed under intraoperative PTH monitoring, and PTH fell from 2233 pg/mL before excision to 172 pg/mL ten minutes after. Histopathology confirmed a benign adenoma weighing 18 g, the diagnosis resting on the absence of capsular and vascular invasion; the Ki-67 index of 3 to 4% was supportive rather than defining. Serum calcium normalized to 9.0 mg/dL by the fourth postoperative day without complications. Here the nonspecific symptoms were initially attributed to physical training and protein supplementation, and calcium was not measured until the disease was advanced. The frequency of this diagnostic pattern cannot be established from a single case. What the case does show is that concordant multimodality localization enabled focused surgery for an adenoma of unusual size and anatomical extent.