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-operative	DOS pre-operative	POD 0	POD 1	POD 2	POD 3	POD 4	POD 5	12 weeks post-operative	1 year post-operative
Serum Ca (8.7–10.7 mg/dL)	9.1	9.8	9	8.1	7.9	8.2	8.9	9	9.7	9.7
Phosphorus (2.5–4.5 mg/dL)	1.6	1.6	2.1	1.4	1.7	2	2	2.6	3.3
Urine Ca/Cr (12–244 mg/g Cr)	<1		19	9	<1	<1	11	56
Urine P/Cr (54–860 mg/g Cr)	<1		644	458	750	863	516	<1
Alkaline phosphatase (30–115 U/L)	223	177		132					196	76
Vitamin D 1,25-OH2 (18–72 pg/mL)	45		29	45	90	142	77	123	89
PTH (14–64 pg/mL)	127		93	136	217	203	215	50	59
FGF23 (<180 RU/mL)	502	819		974	563	606	707	598
Intact FGF23 (<59 pg/mL)			<14	<14	<14	<14	<14	<14

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