Case Report

Atypical Fragility Fractures due to Bony or Soft Tissue Phosphaturic Mesenchymal Tumors: A Report of Two Cases

Table 1

Pre- and post-operative blood and urine laboratory values for Case 2. Excess FGF23 produced by a PMT promotes renal phosphate excretion and suppresses the production of active vitamin D (1,25-OH2-Vitamin D), leading to renal phosphate wasting, hypophosphatemia, elevated alkaline phosphatase, and secondary hyperparathyroidism. The rapid fall in intact FGF23 after tumor removal induces a rebound in 1,25-OH2-Vitamin D production and increased calcium requirements as the skeleton begins to remineralize. Concurrently, renal phosphate excretion decreases, and blood phosphate levels return to normal [17].

Laboratory results (normal)18 weeks pre-operativeDOS pre-operativePOD 0POD 1POD 2POD 3POD 4POD 512 weeks post-operative1 year post-operative

Serum Ca (8.7–10.7 mg/dL)9.19.898.17.98.28.999.79.7
Phosphorus (2.5–4.5 mg/dL)1.61.62.11.41.7222.63.3
Urine Ca/Cr (12–244 mg/g Cr)<1199<1<11156
Urine P/Cr (54–860 mg/g Cr)<1644458750863516<1
Alkaline phosphatase (30–115 U/L)22317713219676
Vitamin D 1,25-OH2 (18–72 pg/mL)452945901427712389
PTH (14–64 pg/mL)127931362172032155059
FGF23 (<180 RU/mL)502819974563606707598
Intact FGF23 (<59 pg/mL)<14<14<14<14<14<14

DOS = day of surgery; POD = post-operative day.