Effective localization in tumor-induced osteomalacia using 68Ga-DOTATOC-PET/CT, venous sampling and 3T-MRI

Abstract

SummaryTumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting leading to hypophosphatemia due to excessive actions of fibroblast growth factor 23 (FGF23) produced by the tumors. Although the best way of curing TIO is complete resection, it is usually difficult to detect the culprit tumors by general radiological modalities owing to the size and location of the tumors. We report a case of TIO in which the identification of the tumor by conventional imaging studies was difficult. Nonetheless, a diagnosis was made possible by effective use of multiple modalities. We initially suspected that the tumor existed in the right dorsal aspect of the scapula by 68Ga-DOTATOC positron emission tomography/computed tomography (68Ga-DOTATOC-PET/CT) and supported the result by systemic venous sampling (SVS). The tumor could also be visualized by 3T-magnetic resonance imaging (MRI), although it was not detected by 1.5T-MRI, and eventually be resected completely. In cases of TIO, a stepwise approach of 68Ga-DOTATOC-PET/CT, SVS and 3T-MRI can be effective for confirmation of diagnosis.Learning points:TIO shows impaired bone metabolism due to excessive actions of FGF23 produced by the tumor. The causative tumors are seldom detected by physical examinations and conventional radiological modalities.In TIO cases, in which the localization of the culprit tumors is difficult, 68Ga-DOTATOC-PET/CT should be performed as a screening of localization and thereafter SVS should be conducted to support the result of the somatostatin receptor (SSTR) imaging leading to increased diagnosability.When the culprit tumors cannot be visualized by conventional imaging studies, using high-field MRI at 3T and comparing it to the opposite side are useful after the tumor site was determined.

FGF-23 transmitted tumor – induced hypophosphatemic osteomalacia: A rare case of a young woman with recurrent fractures and review of the literature

“…The rather new modality of 68 Ga-DOTA-TOC-PET/CT-scan (using ocreotide as mentioned above) is most sensitive in finding the underlying tumors [14] , [37] , [38] but fails to identify the mass in up to 30–40% [4] . As demonstrated in our case, a stepwise diagnostic approach can be effective, including 68 Ga-DOTA-TOC-PET/CT-scan, venous sampling for FGF-23 levels and localized MRI of the suspected region [39] .…”

Phosphaturic mesenchymal tumor: Case report

“…Although PMTs manifest ultrastructural features of neuroendocrine tumors, they typically lack the immunohistochemical markers of neurosecretory tumors that typically consist of S-100, neuron-specific enolase, chromogranin, and synaptophysin markers. In a systematic process following GaTate testing for localization, systemic venous sampling should be recommended for proper confirmatory testing of serum FGF23 levels, followed by functional MR imaging for direct tumor characterization [9], [10], [11]. In contrast, the currently presented case never required these methods of localization due to previous identification and localization on prior imaging with symptom onset being coincidentally near the time of identification.…”

Clinical Applications of Somatostatin Receptor (Agonist) PET Tracers beyond Neuroendocrine Tumors

“…Small studies by Agrawal et al [ 46 ] and Jadhav et al [ 47 ] also reported higher sensitivity and specificity for SSTR tracers compared with [ 18 F]FDG. Multiple other case and small studies summarized in Table 2 report localization of culprit lesions in patients with TIO using SSTR tracers [ 14 , 38 , 39 , 40 , 41 , 42 , 44 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. An example showing culprit lesions identified in 3 patients using [ 68 Ga]Ga-DOTATATE PET-CT from a small study by John et al [ 38 ] is shown in Figure 5 .…”