Teresa Esposito, Gianpaolo De Filippo, Libuse Tauchmanovà, Giuseppe Mossetti, Luigi Insabato, Fernando Gianfrancesco, Riccardo Muscariello, Michele Cioffi, Pasquale Strazzullo, Domenico Rendina, Annamaria Colao, Rendina, Domenico, De Filippo, G, Tauchmanovà, L, Insabato, Luigi, Muscariello, R, Gianfrancesco, F, Esposito, T, Cioffi, M, Colao, A, Strazzullo, Pasquale, Mossetti, Giuseppe, Rendina, D., DE FILIPPO, G., Taumachmanovà, L., Insabato, L., Muscariello, R., Gianfrancesco, F., Esposito, T., Cioffi, Michele, Colao, A., Strazzullo, P., and Mossetti, G.
To evaluate serum levels of osteoprotegerin (OPG), soluble receptor activator of the nuclear factor-kappa B (RANKL), and their relationship with FGF-23, lumbar bone mineral density (BMD), and bone turnover markers, five patients with tumor-induced osteomalacia (TIO) and 40 healthy controls were studied. TIO patients were followed for 360 days after surgical removal of underlying tumor (n = 2) or beginning of therapy with phosphate and calcitriol when surgical treatment was impossible (n = 3). At diagnosis, TIO patients had higher levels of FGF-23 and bone-specific alkaline phosphatase (bALP) and lower levels of cathepsin K (CathK), RANKL, and RANKL/OPG ratio compared to controls. During the follow-up, FGF-23 decreased significantly only in patients who underwent a surgical excision, while phosphate and BMD increased in all patients. The increases in BMD, phosphate, and renal phosphate reabsorption rate were directly related. In the first 60 days of follow-up, we observed a prolonged inhibition of RANKL, CathK, and bone resorption markers associated with a persistence of TIO symptoms and an increase in bALP. From day 60, levels of bone turnover markers returned progressively within the normal range and a clinical remission was observed. The inhibition of the RANKL/OPG pathway and the uncoupling of bone formation and resorption observed in patients with active TIO may be a compensatory mechanism, attempting to reduce worsening of osteomalacia. The BMD increase during TIO treatment is related to the improvement of phosphate rather than FGF-23 levels. A "hungry bone"-like syndrome was observed after surgical or pharmacological treatment.