A Case of a Hypophosphatemic Osteomalacia Secondary to FGF23 Producing Mesenchymal Tumor

Program: Abstracts - Orals, Poster Previews, and Posters
Session: FRI 368-390-Metabolic Bone Disease Case Reports (posters)
Clinical
Friday, April 1, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board FRI 382
Luke Conway*1, Jennifer Y Yarker2, Leonie Reading3 and Ashim Kumar Sinha4
1Cairns Hospital, Cairns. QLD, Australia, 2Cairns Hospital, Cairns QLD, Australia, 3Pathology Queensland, Cairns QLD, Australia, 4Cairns Hospital. James Cook University, Cairns QLD, Australia
Background

Fibroblast Growth Factor 23 (FGF23) is a phosphaturic hormone.  Rarely FGF 23 is produced by soft tissue mesenchymal tumors causing hypophosphatemic osteomalacia. 

Clinical Case

A 79 year old male was referred with a 12 month history of bone pain.  Initial investigation noted severe hypophosphatemia with serum phosphate of 7.2mg/dL (14-27) and raised urinary phosphate 185mg/dL/day (44.8-134.4). Corrected and ionised calcium level were normal.  Further investigation demonstrated an inappropriately normal 1,25 vitamin D level 2.7ug/dL (2.1-7.5) and normal PTH 0.49ng/dL (0.1-0.5). His rib, left knee and ankle pain was evaluated with a bone scan that demonstrated multiple minimal trauma fractures. Screening for secondary causes of osteoporosis was otherwise unremarkable.  PET Ga-68 Dotate scan showed an intensely avid lesion overlying the dorsum of the foot that was confirmed on further MRI imaging to be overlying the tibialis anterior.

One tablet three times day of sandoz phosphate and two tablets a day of Calcitriol were commenced with improvement in his symptoms and serum phosphate.  Excision of the lesion confirmed a soft tissue mesenchymal tumor that stained positively for FGF23.  Following resection of the tumor his oral phosphate and vitamin D supplementation was ceased.  He remained asymptomatic with normal electrolytes.

Conclusion

Mesenchymal tumors that produce FGF23 should be considered as a rare cause of osteomalacia if associated with hypophosphatemia and raised urinary phosphate in patients with bone pain or minimal trauma fractures.

Nothing to Disclose: LC, JYY, LR, AKS

*Please take note of The Endocrine Society's News Embargo Policy at https://www.endocrine.org/news-room/endo-annual-meeting/pr-resources-for-endo