Patient Background: A 79-year-old woman presented with persistent hypophosphatemia (serum phosphorus 0.8 mg/dL) and multiple stress fractures involving the ribs, spine, and pelvis, consistent with osteomalacia. Her medical history included type 2 diabetes mellitus, hypertension, obesity, osteoarthritis, and anxiety disorder.

Assessment and Diagnosis: Initial evaluation revealed severe hypophosphatemia (0.8 mg/dL; NR: 2.5–4.5 mg/dL), elevated parathyroid hormone (PTH, 169 pg/mL; NR: 10–65 pg/mL), and normal serum calcium levels. Despite vitamin D supplementation, hypophosphatemia persisted (1.7 mg/dL in 2023), and hypercalcemia developed later (10.9 mg/dL; NR: 8.5–10.2 mg/dL). Renal studies showed phosphate wasting (tubular reabsorption of phosphate [TRP] 56.2%) and elevated fibroblast growth factor 23 (FGF-23, 1694 kRU/L). In 2024, ^18F-fluorocholine PET-CT imaging identified two right parathyroid adenomas, confirming a diagnosis of primary hyperparathyroidism (PHPT).

1. How can chronic hypophosphatemia signal early-stage PHPT?
2. Why is postoperative monitoring vital in PHPT care?