Concordance Between Whole-Body Scintigraphy 111In-Octreotide and 99mTc-Sestamibi Uptake in the Detection of Four Tumor-Induced Osteomalacia Cases

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome in which tumors secrete phosphaturic factors such as fibroblast growth factor-23, which increases renal phosphate excretion, causing hypophosphatemia and osteomalacia. These tumors have mesenchymal origin and are usually small and slow growing, and they can be located anywhere in the body. Because the cure for TIO includes its total resection, the challenge of the treatment is to locate it (1). Once TIOs express somatostatin receptor subtypes 2 and 5, 111In-octreotide (especially if combined with SPECT/CT [single photon emission computed tomography/computed tomography]) and more recently 68Ga-DOTANOC PET/CT (positron emission tomography/CT) and 68Ga-DOTATATE PET/CT have been shown to be excellent in their detection (2). Because TIOs are highly vascular, 99mTc-sestamibi scintigraphy (MIBI) has also been used for this purpose (3–5). We follow four patients (three women and one man; ages 12–46 y) whose clinical picture and laboratorial data suggested hypophosphatemic osteomalacia, which was confirmed by bone histomorphometry. They underwent whole-body scintigraphy 111In-Octreotide (Octreoscan) and 99mTc-sestamibi to localize the tumor. Both methods revealed that the same body areas of focally increased tracer uptake in different anatomical sites in each patient (right leg, left foot, left leg, and left knee) were visualized in detail with magnetic resonance image (Figure 1). Histopathological findings after the tumor's resection confirmed the existence of phosphaturic mesenchymal tumor, a mixed connective tissue variant. In these four patients, both methods (whole-body scintigraphy 111In-octreotide and MIBI) detected TIOs. For this reason, when Octreoscan is not available, we encourage TIO screening by MIBI. A, Three- and 24-hour 111In-octreotide scan; B, 30-minute whole-body scintigraphy 99mTc-sestamibi; and C, magnetic resonance image longitudinal sections. The arrows reveal focally increased tracer uptake (A and B) and point to tumoral localization (C). Patient 1, female; age, 29 years; mass of 4.7 × 1.7 × 1.8 cm in the right leg. Patient 2, female; age, 67 years; lesion of 2.0 × 1.2 × 1.2 cm in the left foot. Patient 3, female; age, 29 years; mass of 4.7 × 2.7 × 2.1 cm in the left leg. Patient 4, male; age, 25 years; tumor of 4.5 × 2.5 × 0.7 cm in the left knee. M.P.F. is supported by a doctoral fellowship from CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior). Disclosure Summary: The authors have nothing to disclose. computed tomography 99mTc-sestamibi scintigraphy positron emission tomography single photon emission computed tomography tumor-induced osteomalacia.