Anatomical distribution and sclerotic activity of bone metastases from thyroid cancer assessed with F-18 sodium fluoride positron emission tomography

Currently, bone scintigraphy (BS) is considered to lack sensitivity in dete cting bone metastases (BM) from thyroid cancer. We evaluated the anatomical distribution and metabolic behavior of BM as well as the accuracy of BS wi th and without combination of whole-body iodine scintigraphy (WBI) in detec ting metastatic bone disease in thyroid carcinoma. F-18 positron emission t omography (PET), x-ray, BS, and WBI were performed in 35 patients with know n or suspected bone metastases from papillary (9 patients) or follicular (2 6 patients) thyroid carcinoma. Twenty-two metastases were previously known in 14 patients. The indication was staging in 21 patients with high risk fo r BM, elevated thyroglobulin (Tg)-levels or evaluation of exact extent of B M (14 patients). In addition, results of WBI (35 patients), X-ray (35 patie nts) F-18 PET (35 patients), MRI of the spine (13 patients), and FDG-PET (1 5 patients) as well as the clinical course (1.5-4 years) were correlated. B M were detected in 18 patients. Solitary, bifocal, or multiple lesions were present in 9, 2, and 7 patients, respectively. The anatomical distribution of BM (n = 43) was as follows: spine, 42%; skull, 2%; thorax, 16%; femur, 9%; pelvis, 26%; humerus and clavicle, 5%. Sensitivity of BS in interpretin g patients as positive or negative for having BM was 64%-85% (specificity, 95%-81%). The combination of BS and WBI was 100% sensitive in detecting met astatic bone disease. One patient had a single BM that was positive at BS b ut negative on WBI. All metastases were osteolytic on x-ray and two-thirds presented a missing or very limited osteosclerotic bone reaction on F-18 PE T. Our data confirm the limited sensitivity of planar BS in detecting BM fr om thyroid cancer. The combination of BS and WBI, however, was highly accur ate. Compared to other malignancies, the distribution pattern of BM present ed a lower percentage of vertebral metastases and more patients with single metastases. Those findings in combination with a missing or only slight os teosclerotic bone reaction explain the limited sensitivity of planar BS alo ne.