99mTc-HYNIC-TOC in the Evaluation of Recurrent Tumor-Induced Osteomalacia

Purpose Tumor-induced osteomalacia (TIO) is rare paraneoplastic disorder generally caused by small benign neoplasm. Somatostatin receptor imaging has emerged as imaging of the choice in the localization of the causative tumors in new patients with clinical diagnosis of TIO. An accurate localization of the causative tumor using somatostatin receptor imaging followed by successful surgical removal offers cure of the disease. In small percentage of the patients, however, there can be recurrent disease after the surgery. In this retrospective investigation, we tried to assess whether somatostatin receptor imaging using Tc-99m-HYNIC-TOC (Tc-99m-hydrazinonicotinyl-Tyr3-octreotide) is also useful in patients with recurrent TIO after initial successful surgery. Methods The images of Tc-99m-HYNIC-TOC images and clinical charts of total 18 patients with suspected recurrent TIO were retrospectively reviewed. The image findings were compared with the clinical chart, which include clinical follow-up and subsequent imaging and surgery. Results Among all 18 patients, Tc-99m-HYNIC-TOC imaging results were negative in 5 of them. Among these 5 patients with negative imaging study, the causes of recurrent symptoms and hypophosphatemia in 3 patients were eventually found unrelated to TIO. Tc-99m-HYNIC-TOC successfully identified either recurrent causative tumors in the same location (n = 10) or different causative tumor in other locations (n = 3) in 13 patients, which rendered a sensitivity of 86.7% (13 of 15). Conclusions The efficacy of Tc-99m-HYNIC-TOC imaging in the evaluation of patients with potential recurrent TIO is compatible to that with new patients who never received surgical resection for the culprit tumors. It can play an important role in known TIO patients who were suspected to have recurrent disease.