MON-504 Osteomalacia During Pregnancy: Are Preventive Measures Enough to Avoid Future Fractures and Fetal Complications?

Title Osteomalacia during pregnancy; are preventive measures enough to prevent future fractures and fetal complications? Background We present a patient with a left hip fracture found to have FGF-23 induced osteomalacia whose clinical course was complicated by pregnancy. Clinical Case A 28 year old female with a history of iron deficiency anemia presented with left hip pain resulting in difficulty ambulating. Nine months prior, she had suffered a fall at home where she slid down nine steps on her left side, she developed pain in her left leg that prompted her to seek care in multiple emergency rooms; she was given acetaminophen for pain only. Seven months after the fall she started limping requiring a cane to ambulate, a week before admission, she had another mechanical fall where she slipped and fell landing again on her left hip after which she sought care. Further history revealed no regular intake of any medication including no inhaled or systemic steroids, regular menses and no symptoms of hyperthyroidism or malabsorption. Physical exam was pertinent for limited range of motion of her left leg. Blood tests were significant for alkaline phosphatase (ALP) 220 [30-95U/L], phosphorus 2.1 [2.5-5.0mg/dL], 25-OH vitamin D 14.80 [30-95pg/mL], Vitamin D 1,25(OH)2 <8 [18-72pg/mL], and Fibroblast Growth Factor 23 (FGF-23) 1241 [<180RU/ML]. Other labs included: Calcium 9.3 [8.2-10mg/dL], albumin 4.28 [3.5-5.70 g/dL], PTH 37.9 [15.0-65.0pg/mL], ALP isoenzymes: total ALP 202 [33-115 U/L], liver 44 [25-69%], bone 56 [28-66%], 24hr urine phosphorus 0.5 [0.3-1.3g/24hr] with under collected specimen , volume 1 liter and creatinine 0.9 [1-2 g/24hr], TSH 2.54 [0.35-4.70 uI/mL], cortisol after 1mg Dexamethasone was 0.3 [<1.8 mcg/dL]. The grossly elevated FGF-23 lead to a suspicion of tumor-induced osteomalacia, Imaging revealed stress fractures of the left aspect of the sacrum and left femoral neck. A bone scan was significant for diffuse lesions and bone densitometry showed osteoporosis in the lumbar region with a Z score of-2.5 and osteopenia of lumbar and femoral neck Z -1.9. Femoral neck biopsy was negative for malignancy. She underwent percutaneous pining of the femoral neck and was discharged with calcitriol, cholecalciferol and phosphate supplementation. An Octreotide scan obtained during follow-up was negative. Her phosphate levels have been difficult to manage even with high supplementation of phosphate, and further attempts to localize the tumor have been temporarily held as the patient is now pregnant. Conclusion This patient who initially presented with femoral neck and sacrum stress fractures and diagnosed with osteomalacia and hypophosphatemia allows us to learn and question what the appropriate treatment strategy should be to ensure both patient and fetus are adequately supplemented to prevent any future fractures in the mother and promote normal development of the fetus.