Oncogenic osteomalacia: exact tumor localization by co-registration of positron emission and computed tomography

[Metabolic bone diseases]

Osteomalacia is caused by impaired vitamin D receptor (VDR) signaling, calcium deficiency, and altered bone mineralization. This can be due to insufficient sunlight exposure, malabsorption, reduced D hormone activation in chronic kidney disease, and rare alterations of VDR signaling and phosphate metabolism. Leading symptoms are bone pain, muscular cramps, and increased incidence of falls in the elderly. The adequate respective countermeasures are to optimize the daily intake of calcium and vitamin D3 and to replace active D hormone and phosphate if deficient. Osteoporosis is characterized by bone fragility fractures upon minor physical impact. Indications for diagnosis and treatment can be established by estimating the absolute fracture risk, taking into account bone mineral density, age, gender, and individual risk factors. Exercise, intervention programs to avoid falls, and specific drugs are capable of substantially reducing fracture risk even in the elderly. Secondary osteoporosis primarily requires both bone-altering medications and effective treatment of underlying diseases.

Tumor-induced hypophosphatemic osteomalacia diagnosed by the combinatory procedures of magnetic resonance imaging and venous sampling for FGF23

This report describes a 37-year-old man with tumor-induced osteomalacia (TIO). The patient had hypophosphatemia and elevated fibroblast growth factor 23 (FGF23) in the peripheral blood. Magnetic resonance imaging detected an abnormal mass in the left greater trochanter. Venous sampling revealed a significantly higher level of FGF23 in the left common iliac vein (proximal to the tumor), verifying that the tumor is responsible for TIO. The serum level of FGF23 decreased and symptoms improved after removal of the tumor. The combined diagnostic procedures of MRI and venous sampling for FGF23 effectively detected the tumor responsible for TIO.

Imaging in the investigation of paraneoplastic syndromes

Paraneoplastic syndromes are a heterogeneous group of disease presentations caused by underlying tumours. As they are non-metastatic in nature an intensive diagnostic evaluation is warranted to identify potentially curable lesions. The selection of the appropriate method of imaging is important in these cases, especially when history and physical examination are unrevealing. In this review the important paraneoplastic syndromes and underlying malignancies are discussed along with relevant imaging strategies.

Regulation of phosphate homeostasis in infants, children, and adolescents, and the role of phosphatonins in this process

PURPOSE OF REVIEW

Unlike calcium metabolism, the control of phosphate homeostasis has long been poorly understood. The identification of 'phosphatonins' in the serum of hypophosphatemic patients, the unveiling of the genetic causes of hypo and hyperphosphatemic diseases in patients, and the creation of finely adapted animal models have revolutionized our understanding of phosphate homeostasis.

RECENT FINDINGS

Original reports published in 2006/2007 bring valuable pieces of information that enable better understanding of the physiological regulation of phosphate homeostasis by more precisely defining the interplay between PHEX, vitamin D, and phosphatonins; identification of new genes causing hypophosphatemic rickets, aside from PHEX and fgf23, namely the genes encoding for a renal sodium-phosphate cotransporter, NaPiIIc, and for a bone matrix protein, DmpI; and improved diagnosis of tumor-induced osteomalacia with more precise imaging techniques for tumor localization and more precise fibroblast growth factor 23 assays.

SUMMARY

From a clinical point of view, these findings offer new tools for the diagnosis of hypophosphatemic rickets (biologic, genetic, imaging techniques) and open the way to new treatment strategies.