MON-503 Difficult Decisions in Endocrinology: Unexpected Pregnancy during Diagnosis of TIO

Introduction Fibroblast Growth Factor 23 (FGF23) is a hormone which controls phosphate homeostasis by increasing renal excretion of phosphate and preventing hydroxylation of 25-OH vitamin D. Tumor Induced Osteomalacia (TIO) is a rare condition in which there is exogenous production of FGF23 from tumor cells which leads to hypophosphatemia, progressive muscle weakness and bone fractures. In our case, we present a young pregnant female who presents an ethical dilemma in TIO workup. Case Presentation A 29-year-old Hispanic female with history of anemia, Chiari I Malformation was referred to Endocrine clinic for workup of fractures in the setting of low vitamin D.  She initially presented to an outside hospital after fall and was noted to have “bruised bones.” She came to our ED multiple times for hip and back pain. Imaging showed stress fracture of the femur and lytic lesions in the hips. Bone biopsies were negative. Labs showed decreased alkaline phosphatase, 25-OH vitamin D and phosphate. DEXA scan showed decreased bone density and skeletal survey with diffuse bone loss and osteomalacia. Secondary causes of metabolic bone disease were ruled out. Of note FGF23 was markedly elevated, but octreotide scan to did not reveal a tumor reflective of TIO. While workup was being done, patient was treated with aggressive phosphate, magnesium, and calcitriol repletion. DOTATATE PET was planned for localization of TIO, but patient became pregnant. After further discussion, she agreed to halt further evaluation until delivery. Discussion Radiation and medications are often harmful to the growing fetus. For this reason, diagnostic procedures are often delayed until after the baby is deliver to prevent unnecessary harm to the fetus. In our case, we argue that a potentially diagnostic DOTA-TOC PET/CT scan is crucial for our patient. Overexpression of FGF23 can be either a genetic disorder or an oncogenic disorder called TIO. Treatment for these conditions is different. If a focus for the TIO could be localized, it could be excised, whereas a genetic disorder could be treated with Burosomab. Given the rapid progression of our patient’s disease, progressing from asymptomatic to disabled in less than a year, we were forced to ask ourselves if we could wait for delivery for diagnosis and treatment. On one hand, radiation from the scan will almost guarantee harm or death of the fetus. On the other hand, delay in treatment may lead to irreversible and permanent harm to the mother and possible indirect harm or death of the fetus. There are no guidelines for addressing TIO in pregnancy. We were unable to find any cases of FGF23 elevations during pregnancy. Informed Decision must be made between the patient and the medical team to ensure that the best decision is made for both the mother and the fetus.