Endocrine Abstracts

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of chronic hypophosphatemia caused by the production of FGF23 in a typically small, benign, mesenchymal tumor. The diagnosis is often delayed and finding the tumor is sometimes challenging. We present a case of a 50 yrs old woman with TIO, referred to our clinic for progressive muscle weakness, diffuse bone pain and fractures, extensively investigated for 3 years. 2 years before admission she had a vertebroplasty for severe L5 vertebral fracture and in the last 12 months she suffered multiple moderate thoracic and lumbar vertebral fractures. At presentation she was unable to stand or walk without help. Laboratory findings: hypophosphatemia 1.1 mg/dl, phosphate renal wasting (phosphaturia 0.56 g/l; TmP/GFR = 0.36 mg/dl/l), Alkaline Phosphatase 462 U/l (40–150), normal serum Calcium, 25OHD 20 ng/ml, PTH 58 pg/ml, high bone turnover – CTX 0.640 ng/ml (0.162–0.436), P1NP 152 ng/ml (15–74), osteocalcin 26 ng/ml (11–43); no proteinuria/aminoaciduria/glucosuria, normal urinary electrolytes. The very high FGF23 level (5495 pg/ml, normal range 26–110) in this context suggested the diagnosis of TIO and the patient was referred for 68Ga PET-CT. Despite specific recommendation for whole body scanning, both feet were excluded from imaging exam and no tumor was found. Oral phosphates and alfacalcidol were started, with clinical improvement and modest increase in phosphate levels. At follow-up a plantar tumor was found by palpation in the soft tissue beneath the first left metatarsal, confirmed by ultrasonography and subsequently by MRI. Tumor resection completely resolved the symptoms and rapidly normalized the biochemistries. The biopsy revealed a mesenchymal tumor, with giant osteoclast-like cells, mitoses, areas of osseous metaplasia.

Conclusion

A thorough head-to-toe physical examination and functional imaging are essential for tumor localization.