Endocrine Abstracts

Introduction: Causes of hypophosphataemia include reduced intestinal absorption, inadequate intake, transcellular shifts (refeeding syndrome, glucose/insulin infusion), renal loss which is either FGF23 mediated (inherited forms or tumour induced osteomalacia) or non-FGF23 mediated (hyperparathyroidism, drugs)

Case report: We present a case of 51 years old female referred to us with multiple fractures during her half marathon. She suffered from bilateral metatarsal fractures & had distal fibula fracture in 2017. Her routine blood results revealed low phosphate. She had low phosphate levels since 2019 ranging from 0.41 to 0.63 mmol/l. Her Urine calcium excretion was slightly low and phosphate excretion was within normal range. Her ALP and FGF23 levels were high as below: This pointed towards FGF23 mediated hypophosphataemia likely tumour induced. A whole body SPECT CT scan showed multiple non-specific uptakes at left Clavicle, ribs, both pubic rami and Left foot third metatarsal likely Oncogenic Osteomalacia. Subsequently, an Octreotide/Tektrotyd scan was performed which picked up faint activity at right Pubic symphysis medial to the pectineus muscle about size of 2 cm. MRI scan also spotted a small focus in Right pectineus muscle 17×11mm. After discussion at Soft Tissue/Bone MDT, she underwent resection and biopsy was consistent with phosphaturic mesenchymal tumour. Her phosphate levels have normalized now.

Discussion: Tumour Induced Osteomalacia (TIO) is a rare paraneoplastic syndrome causing muscle weakness, fractures and bone pains. FGF23 is secreted by the mesenchymal tumours & impairs phosphate reabsorption and 1α-hydroxylation of 25-hydroxyvitamin D at renal tubules. Most common tumours are in the skin, muscles, and bones of extremities or paranasal sinuses. First line treatment is surgery, if not feasible then phosphate & Vitamin D supplementation is helpful.