Radionuclide treatment of metastatic disease in patients with differentiated thyroid carcinoma.

In general, the therapy of differentiated thyroid carcinoma (DTC), includes initial treatment and follow-up of patients. Nowadays, there is no universal accepted consensus regarding initial treatment of DTC patients. Several countries have their own guidelines and recommendations for treatment of DTC . Beside all controversies, mostly accepted recommendation regarding initial treatment of DTC includes total or “near” total thyreoidectomy followed by the therapy with radioactive iodine (I). Radioiodine ablation of postoperative thyroid remnants is usually recommended in all DTC patients regardless their stage (low or high risk of cancer-specific mortality and risk of relapse), due to easier monitoring of thyroglobulin (Tg) . Thyroglobulin is a glycoprotein that is produced by normal or neoplastic follicular thyroid cells. In the absence of thyroglobulin antibodies (TgAb), undetectable Tg after the thyroid stimulating hormone (TSH) stimulation is a valid parameter of remission and the absence of metastases. On the other hand, detectable or increasing Tg during followup indicates the appearance of metastatic disease. After radioiodine ablation, a life-long suppressive therapy with Lthyroxine should be prescribed to all DTC patients. Rarely, a palliative therapy including external beam radiation therapy and chemotherapy is recommended . After the initial treatment, all DTC patients should be monitored life long, with the aim to detect persistent disease or recurrence. Each check-up should include laboratory analyses (thyroid hormones, TSH, Tg and TgAb) and ultrasonography of the neck. The result of diagnostic whole-body scintigraphy (WBS) with I (I-WBS) is influenced by thyroid carcinoma affinity to accumulate I in the presence of high concentration of TSH achieved by one-month L-thyroxine withdrawal or with intramuscular application of human recombinant TSH . Whole-body scintigraphy is routinely performed as a routine check-up (a year after the radioiodine ablation), and thereafter in cases suspected for recurrence only . Magnetic resonance imaging (MRI) and computed tomography (CT) are useful for detection of neck and mediastinal metastases . Magnetic resonance is useful especially in non-iodineavid and mediastinal metastases . Fluorodeoxyglucose (FFDG) positron emission tomography fused with computed tomography (F-FDG-PET/CT) is a modern diagnostic procedure that is important in detection of non-iodine-avid metastases . Computed tomography is useful in visualization of small lung metastases, but is rarely performed due to iodine contrast interference with iodine therapy .