Endocrine Abstracts

Tumour-induced osteomalacia (TIO) is a paraneoplastic syndrome caused by the overproduction of fibroblast growth factor (FGF23) from a tumour. It is characterised by renal phosphate-wasting, resulting in hypophosphatemia, osteomalacia and fragility fractures. Clinical manifestations are non-specific, often leading to misdiagnosis or delayed diagnosis. A thirty-five-year-old female presented to her GP with bilateral hip/groin discomfort at seven months gestation and was diagnosed with Symphysis Pubis Dysfunction. She experienced worsening bony pain in her ribs and back, particularly after childbirth. She was breastfeeding. An MRI of her hips revealed multiple pelvic ring insufficiency fractures and bilateral femoral neck stress fractures. DEXA scan showed low BMD at the spine and hips (Z-scores: -2.8 and -3.1, respectively). She was referred to the Endocrine Bone clinic, where Pregnancy-Lactation-induced osteoporosis was initially suspected. Blood tests showed ALP bone isoenzyme 73(5-16 units/L), calcium 2.33(2.20-2.60 mmol/L), vitamin D 99.3(50-150 nmol/L), low phosphate 0.45(0.80-1.50 mmol/L). Tubular maximum re-absorption of phosphate to GFR ratio was significantly reduced at 0.32(0.84-1.23 mmol/L), demonstrating a renal phosphate leak. FGF23 level was inappropriately raised at 313(<100 RU/mL) with low 1,25 Vitamin D. Oral phosphate replacement and alfacalcidol were started with some biochemical improvement but continued symptoms. A Gallium DOTATE PET identified a DOTATE avid lesion within the flexor compartment of the upper right thigh. She successfully underwent surgery to remove the lesion with histology in keeping with a phosphaturic mesenchymal tumour. By day 5 post-operatively, her phosphate level had normalised off supplements. Despite presenting with debilitating symptoms and multiple fractures, our patient’s diagnosis was delayed in primary care. Overlapping symptoms led to an early misdiagnosis of SPD and suspicion of PLO. It is vital to raise awareness of TIO so that appropriate and timely investigations and potentially curative surgery are performed.