Endocrine Abstracts

A 71-year-old female with no significant past medical history was referred to endocrinology for persistently low serum phosphate and raised alkaline phosphate levels despite adequate replacement of vitamin D. She reported 10 years history of generalised body aches and muscle weakness. X ray imaging picked up multiple healed rib fractures. No history of childhood rickets, nor family history of hypophosphatemic rickets. She had significant proximal myopathy. Her laboratory workup in the clinic showed serum phosphate of 0.64 (0.8 to 1.5) nmol/l, adjusted calcium of 2.18 (2.2 to 2.6) nmol/l, 25 hydroxyvitamin D of 76 (>50) nmol/l, Parathyroid hormone of 15 (1.6 to 6.9) pmol/l, serum alkaline phosphatase of 390 (30-130) unit/l, serum creatinine of 77 (48-84) umol/l. Initially, a differential diagnosis of partial vitamin D resistance was considered and was commenced on calcitriol 1.5 mg once daily. DXA scan confirmed osteoporosis with T score of -3.6 at femoral neck and -2.3 at lumber spine. Calcitriol replacement normalised her calcium and PTH levels, but serum Phosphate remained low with inappropriately normal 24-hour urine phosphate at 12.6mmols. FGF-23 was elevated at 126 (reference range< 100) RU/ml. Ga 68 DOTATAE whole body PET CT showed avid lesion within the left anterolateral T7 vertebral body and 15 mm lesion was confirmed on MRI whole spine. She was treated with CT guided radiofrequency ablation. Day 4 post procedure, her phosphate levels were within normal range at 0.93nmol/l. Although, the histology was not convincing of phosphaturic mesenchymal tumour, her phosphate levels have remained within normal range off calcitriol for 5 months. Her muscle aches and bony pain have resolved. Repeat FGF-23 has dropped to 57 RU/ml and repeat DXA scan showed significant improvement in bone density with T score of -2.3 at femoral neck and -0.3 at lumber spine