ソマトスタチン受容体シンチと経皮静脈サンプリングで責任腫瘍の局在診断が可能であった腫瘍性骨軟化症（TIO）の一例

We report a case of 57-year-old-female with progressive bone pain and proximal dominant muscle weakness. Laboratory test revealed hypophosphatemia with decreased TmP/GFR, high bone-type ALP and elevated levels of FGF23. Radiograph and CT examination revealed multiple fracture with decreased levels of bone mineral density. She also had 2 cm of subcutaneous elastic soft tumor which located on the base of left big toe. Moreover, somatostatin receptor scintigraphy revealed increase uptake in the tumor with high suspicion of the culprit tumor of tumor-induced osteomalacia （TIO）. To verify that the tumor generates FGF23, we performed percutaneous venous blood sampling. The FGF23 level in the left dorsal vein of foot was highest those in other veins. These results strongly suggested that the tumor produced FGF23 and was the culprit tumor for the disorder. The patient underwent resection of the tumor. One day after surgery, the serum FGF23 level in a peripheral vein decreased to less than the measurement sensitivity, while serum phosphate improved to normal range. Two months of following surgery, clinical and biochemical examinations confirmed the successful of operation. Although it is sometimes difficult to detect the culprit tumors in TIO cases, a combination of localization studies may improve diagnostic accuracy of the culprit tumors. Furthermore, percutaneous peripheral venous sampling would be clinically useful for cases who have the responsible tumor located on limbs, hands and feet.