Functional imaging modalities enhance localization of tumour-induced osteomalacia
The use of functional imaging modalities such as octreotide scintigraphy and 68Ga DOTATATE PET/CT* enhances localization of tumour-induced osteomalacia (TIO), a rare syndrome characterized by bone pain, muscle weakness, and skeletal deformities due to overproduction of the hormone fibroblast growth factor 23 (FGF23), according to data presented at AFOS 2017.
Octreotide scanning is ‘a very important scan’ and has been routinely used for suspected TIO given its efficiency in tumour detection, said Dr Weibo Xia from the Peking Union Medical College in Beijing, China.
On the other hand, although not frequently used, 68Ga DOTATATE PET/CT has been shown to further improve the detection rates to about 97 percent, added Xia. “If the [tumour] cannot be found with routine octreotide scanning, we [shift to] 68Ga DOTATATE PET/CT.” [AFOS 2017, abstract PL007]
Octreotide scanning has a high affinity for somatostatin receptors found in TIO, [Clin Nucl Med 2008;33:752-756] while 68Ga-DOTATATE PET/CT utilizes a modified octreotide molecule that has an increased affinity for both somatostatin receptor 2 and 5. [Eur J Nucl Med Mol Imaging 2003;30:1338-1347; Eur J Nucl Med Mol Imaging 2005;32:724; Endocr Relat Cancer 2011;18:R53-R77]
Relying on physical examination or laboratory analysis may not be sufficient to identify TIO tumours, as these are typically small and grow slowly. Additionally, the nonspecific imaging manifestations of TIO further increases the degree of difficulty of localizing tumours, hence the need for more advanced alternatives, said Xia.
Furthermore, the high likelihood of misdiagnosis in TIO given its similarities with nonspecific hypophosphatemia underscores the importance of utilizing the appropriate imaging modality in localizing TIO, as this will aid in determining the suitable treatment approach, he added.
While an MRI scan may be ideal for identifying TIO tumours, it could be difficult, noted Xia. “[In some cases], patients may have high levels of [parathyroid hormones] and hypoparathyroidism might be suspected.”
Failure to completely localize the tumour may require supplementation with phosphorus and calcitriol and, should this fail, complete surgical resection, he added.
“Complete resection of the tumour may dramatically decrease FGF23 in a matter of hours,” said Xia. In 2–6 months, complete symptomatic relief may be achieved by reducing the excessive FGF23, thereby leading to the downregulation of phosphate and vitamin D and eventually, hypophosphatemia, he added.
Despite being a potential treatment alternative for TIO, curettage is associated with a high recurrence rate that would eventually require secondary segmental resection, added Xia.