Endocrine Abstracts

Introduction: Vitamin D deficiency is increasingly being recognized as a widely prevalent metabolic disorder in temperate climates with various systemic manifestations. However topical, it is important to exclude tumour induced osteogenic osteomalacia as a possible aetiology in severe vitamin D deficiency when other risk factors (vegetarian diet, ethnicity, etc.) are absent. Early diagnosis of malignant tumours could be life saving and their resection may make this vitamin D resistant syndrome respond to treatment. We would like to introduce and discuss the importance of fibroblast growth factor-23 (FGF-23) as a tumour marker and a possible paraneoplastic substance.

Case report: A 58-year-old Caucasian man presented to his general practitioner with severe back pain and very low vitamin D3 levels (<10 nmol/l). Alkaline phosphatase was elevated at 160 U/l and over the next few months his calcium levels decreased to a low of 2.06 mmol/l and phosphate to 0.76 mmol/l. He was prescribed vitamin D supplements and subsequently a Tc-99m bone scan revealed marked increased activity in the right proximal femur indicating an aggressive osteoblastic process, in-keeping with osteosarcoma. The femur was resected and a titanium implant inserted.

Discussion: Osteogenic osteomalacia is a very rare diagnosis with subtle manifestations, which can be a consequence of an underlying indolent neoplasm. Undetected, the associated malignant tumours could metastasize. A high degree of clinical awareness and suspicion is required, particularly if the tumour is small along with the use of radiological investigations such as PET and Octreotide scans to detect occult tumours. FGF-23 is a member of the FGF family, which is involved in phosphate homeostasis and skeletogenesis and may prove useful as a tumour marker to help exclude a malignant tumour in severe vitamin D deficiency.