case_images: PMC10576504_01
case_images: (a) Contrast-enhanced CT from the cervical to pelvic region revealed a 6x4 mm tumor on the anterior surface of the right scapula and a 13 mm tumor in the right parotid gland (indicated by circles). (b) 18FDG PET/CT showed FDG accumulation on the anterior surface of the right scapula (SUVmax: 3.5) and in the right parotid gland (SUVmax: 6.3) (indicated by circles).
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case_images: Contrast-enhanced computed tomography (CT) revealed a 6 x 4 mm tumor on the anterior surface of the right scapula, and a 13 mm tumor in the right parotid gland (Figure 1a). 18FDG PET/CT showed FDG accumulation at the same site as the tumors on the anterior surface of the right scapula (SUVmax 3.5) and in the right parotid gland (SUVmax 6.3) (Figure 1b), although qualitative evaluation and tumor differentiation were difficult with 18FDG PET/CT.
case_images: (a) FGF23 levels obtained in the first venous sampling. The values are shown in pg/mL. FGF23 was highest in the right subclavian vein. (b) Second venous sampling showed that FGF23 was higher in the right subclavian vein than in the right external jugular vein, suggesting that the tumor on the anterior surface of the scapula was the responsible tumor.
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case_images: To identify the responsible tumor, venous sampling of FGF23 levels was performed at 26 locations throughout the body, which revealed significantly high FGF23 levels in the right subclavian vein (Figure 2a). Therefore, venous sampling was performed again in the upper body, including the external jugular vein (Figure 2b).
case_images: Subsequent changes in serum phosphorus levels. Burosumab was administered once per month and phosphorus measurements were performed 2 weeks after each administration. Serum phosphorus levels were observed to increase after the first dose of burosumab, and subsequently remained within the normal range from the second dose onwards.
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case_images: Figure 3 shows the subsequent changes in phosphorus levels, which gradually increased with each dose, remaining above normal limits from the second dose onwards.