Bone radioiodine (RAI) uptake without structural abnormality in thyroid cancer (TC) patients may be related to false positive or to microscopic foci of metastatic tissue. In such cases, outcome is reported to be excellent. Mrs D. had been operated for a pT3(m) poorly differentiated TC at the age of 43. The first post-therapeutic whole body scan revealed 3 foci of bone uptake (right clavicle, L2, L3). The elevated level of thyroglobulin (157 ng/mL) favoured the hypothesis of bone metastases despite the absence of any structural lesion on CT and MRI. She received 7 courses of radioiodine therapy. The right clavicle RAI uptake persisted, and subsequent CT disclosed an osteolytic lesion which was treated by radiofrequence and external beam radiation. Twenty-five years after the diagnosis, she has a persistent morphological disease with a 30×8 mm progressive lesion on the right clavicle, for which surgery is planned. In the Nuclear Medicine Departement database, we identified 13 other cases of RAI-avid bone metastases without structural correlation on CT or MRI between 1993 and 2018. After a median follow-up of 3.9 years (range 0.6 to 25 years), 13 patients were alive, one patient had died from a breast cancer. Patients received on average 2.3 courses of radioiodine (median 2, sd 1.5). At last follow-up the disease status was: complete remission in 9 patients (64%), persistance of bone RAI uptake in 1 patient (7%), and structural residual disease in 4 patients (28.5%). Among these 4 patients, 2 had relived from bone metastases, but developed soft tissue metastasis consisting of supra sternal mediastinal nodes (the patient who died from a breast cancer) and lung metastases. One patient had a multimetastatic disease (7%), and Mrs D. had a structural bone metastase with skeletal-related event. Robenshtok et al. reported a similar series of patients with RAI-avid bone metastases of TC without structural abnormality on imaging studies. They concluded that this subgroup of bone metastatic patients have more favorable long-term prognosis than those harbouring structurally visible bone metastases and do not undergo skeletal-related complications. Based on our experience, we agree that most of these RAI-avid bone metastases with no structural correlate often resolve following RAI treatment without serious prognostic significance. However some patients do no achieve remission, and may in rare cases suffer from unfavourable outcomes with skeletal-related complications. In the absence of identified prognosis factors, close follow-up of these patients seems reasonable.
18 - 21 May 2019
European Society of Endocrinology