Effective detection of the origin which cause tumor-induced osteomalacia (TIO) by [Tc-99m]-HYNIC-octreotide (99mTc-HYNIC-TOC) scintigraphy

Objectives Tumor-induced osteomalacia is a rare endocrine disorder and only less than 130 cases worldwise were reported previously in English literature. Since these tumors are generally small slow-growing benign mesenchymal tumors which produce excessive phosphate-transportation-inhibiting growth factors and hormones , the symptoms are mainly related to osteomalacia. The only cure of the disease depends on resection of the tumor, which is extremely difficult using conventional imaging modalities due to its small size and rare locations. Most TIO patients suffered symptoms many years prior to correct diagnoses. Since these tumors are known to express somatostatin receptors, this research was undertaken to evaluate efficacy of [Tc-99m]-HYNIC-octreotide (99mTc-HYNIC-TOC) imaging in this clinical setting.

Methods 75 cases (35 males, 40 females; age range: 17 to 69 years) with clinically suspected TIO had Tc-99m]-TOC scans. The scan results were compared to histopathological examinations (for all positive scans) and clinical follow-up (most negative studies).

Results Forty-eight patients were proven to have TIO while 27 do not have TIO. 99mTc-HYNIC-TOC scintigraphy successfully identified 46 patients suffering TIO The tumors were located in soft tissue of lower extremity (27 cases), bone (13 cases) and craniofacial regions (6 cases) respectively. The scan did not reveal one small (5 mm) lesion in the right thigh and another in the gum. The sensitivity of 99mTc-HYNIC-TOC in this clinical setting is therefore 95.8% (46/48). 99mTc-HYNIC-TOC scintigraphy also excluded 24 patients without TIO with a specificity of 88.9% (24/27). The false positive studies were caused by fracture in 1 and granulomas in 2 cases. The accuracy of 99mTc-HYNIC-TOC scintigraphy in the localization of tumors which cause osteomalacia is 93.3%.

Conclusions 99mTc-HYNIC-TOC scintigraphy is very effective in the localization of occult mesenchymal tumors which cause TIO