Introduction: Oncogenic osteomalacia (OOM) is an uncommon disorder characterized by hyperphosphaturia, hypophosphatemia, decreased vitamin D3 serum levels, and osteomalacia. The paraneoplastic syndrome is driven by a small somatostatin receptor (sstr)-positive tumor that produces phosphatonins. While it is almost always difficult to detect the tumor by common imaging techniques, PET-CT using the radiotracer 68Ga-DOTANOC represents a novel diagnostic approach which facilitates a precise and rapid localization of the associated lesion.
Materials and methods: 2 female patients (age 46 and 63 yrs) complained of severe back pain, atraumatic metatarsal fractures, general muscle weakness, and reduced physical activity for more than one year. Both patients had a high suspicion of OOM because of very low serum phosphate levels, hypophospaturia, and normal PTH. In either case, a careful search for the tumor was initiated by standard imaging techniques as well as PET-CT co-registration using the novel octreotide-derived radiopharmaceutical compound 68Ga-DOTANOC, which has an improved affinity to sstr 2 and 5.
Results: While all routinely used imaging techniques such as CT or MRI were not capable to localize the tumor, only PET-CT co-registration using 68Ga-DOTANOC revealed the exact tumor localization in the right femoral head in both cases. All symptoms were rapidly reversed upon tumor resection and biochemical parameters returned to normal.
Conclusions: 68Ga-DOTANOC-based PET-CT is a novel and powerful approach to detect sst-positive tumors and to provide highly resolved images facilitating the development of a therapeutic strategy.