Endocrine Abstracts

A case of a 29-year old woman presented with a 6-year history of bone pain located in the lower spine and gradually extended to the spinal skeleton and the lower extremities, worsening by activity. The progressive symptoms and the established weakness finally led to patient’s complete disability. The investigation revealed low serum phosphorus and elevated 24 h urinary phosphate excretion, normal serum calcium and 24 h urine calcium excretion, normal to normal-high PTH and elevated serum alkaline phosphatase, particularly the bone isoenzyme. Calcidiol levels were normal and calcitriol values were low. Iliac bone biopsy showed osteomalacia. Renal phosphate wasting can occur in disorders of vitamin D metabolism, in the Fanconi syndrome or in primary phosphaturic syndromes, which can be inherited or acquired, either as idiopathic disorders or in association with mesenchymal tumors (tumor-induced osteomalacia TIO). TIO is more likely to be the diagnosis for this patient based on symptoms and the above findings (osteomalacia, acquired hypophosphatemia, renal phosphate wasting, inappropriately low plasma calcitriol concentration, negative family history). The major diagnostic challenge was the identification of the primary tumor. The scintigraphy using indium-111 labeled octreotide was negative. The total body CT scan showed a soft tissue mass, extensive osteolysis of the ala and the body of the left ilium and extension to the ipsilateral limbus of the acetabulum. FGF23, a potential phosphaturic hormone which has been implicated in TIO, was highly elevated in our patient (1625 RU/l normal values <100). She was treated with calcitriol 3 μg/day, phosphate 3 gr/day and calcium 1500 mg/day until the removal of the causative tumor, with substantial improvement. The surgical resection of the tumor took place at the Royal National Orthopeadic Hospital, Stanmore-Middlesex. The histology demonstrated a phosphaturic mesenchymal tumour without a high-grade component. The excision of the tumor led to reversal of the biochemical and the clinical abnormalities. Unfortunately, FGF23 levels were not measured postoperatively.