Category: Calcium/Bone Disorders
Objective : Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by bone pain, fractures and muscle weakness. Since the symptoms are nonspecific and phosphate levels are not routinely included in metabolic panels, the diagnosis is often delayed or missed. We present a case of acquired chronic hypophosphatemia due to renal phosphate wasting with inappropriately normal fibroblast growth factor 23 (FGF23) levels consistent with tumor-induced osteomalacia.
Methods : 62-year-old female referred to our clinic for evaluation of bone health in 1/2017 given history of low impact fractures of bilateral sacral ala. She also has a history of slow healing fractures in multiple other areas as well as persistent musculoskeletal pains and weakness, to the point where she can now barely stand without support and uses a walker. Prior to these events she was in good health and active woman. Evaluation of secondary causes of osteoporosis revealed a significantly low serum phosphorus level of 1.6mg/dl (2.5-4.5) which was confirmed on repeat testing. Serum calcium, 25-OH Vit D and PTH were in normal range. 1,25 OH Vit D was low normal at 26 pg/mL (18 to 78). 24-hour urinary phosphorus excretion was found to be inappropriately elevated on two occasions. Tubular reabsorption of phosphate was calculated to be 44% (75-98%) confirming renal phosphaturia. FGF 23 level ranged between 119 to 183 RU/mL (<180) indicating likely tumor induced osteomalacia. Fanconi syndrome was ruled out after extensive biochemical evaluation. When a PET/CT did not show any focal masses, she underwent Octreotide scan that revealed uptake in the nasal septum just below the cribriform fossa. Initial nasal endoscopy failed to reveal any masses. She developed right facial cheek swelling for the past 4 to 5 months.ENT evaluation again revealed septal fullness superiorly on the right and a 3mm white papule on the mucosa anteriorly. FNA of this mass was performed 1 week ago and results pending.
Results : .
Discussion : TIO is caused by over secretion of FGF23 leading to hypophosphatemia and osteomalacia. Lesions are typically small, benign mesenchymal tumors. TIO is associated with a markedly reduced quality of life and functional impairment. Reported length of time from the onset of symptoms to diagnosis ranges from 2.5-28 years. Tumor localization is critical since surgical excision is curative.
This case highlights the importance of considering TIO and including serum phosphate measurements in patients presenting with persistent bone pain, fractures and muscle weakness.
Baystate Medical Center
Dr Canan Gunay received her medical degree from Kocaeli University Medical School, Turkey and completed her residency at St Vincent Medical Center, CT. She is currently a second year fellow at Baystate Medical Center, MA.
She received her medical degree from B. J. Medical College Ahmedabad and has been in practice between 11-20 years.