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The usefulness of fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in differentiated thyroid cancer (DTC) has been demonstrated by many investigators, but in only a small number of studies have FDG-PET images been compared with those obtained using other non-iodine tumour-seeking radiopharmaceuticals. In most of the studies, planar imaging was performed for comparison using thallium-201 chloride or technetium-99m 2-methoxyisobutylisonitrile ((99m)Tc-MIBI). Furthermore, FDG-PET studies were not always performed in the hypothyroid state with increased levels of thyroid stimulating hormone (TSH), which are known to increase FDG uptake by DTC. The aim of this study was to compare the ability of FDG-PET to detect metastatic DTC with that of (99m)Tc-MIBI whole-body single-photon emission tomography (SPET) and post-therapeutic iodine-131 scintigraphy, evaluated under TSH stimulation. Nineteen patients (8 men, 11 women; age range, 38-72 years, mean 60 years; 17 thyroidectomised and 2 inoperable patients following (131)I ablation of the remaining thyroid tissue; 16 papillary and 3 follicular carcinomas) with metastatic DTC underwent FDG-PET whole-body scan (WBS) and (99m)Tc-MIBI SPET WBS at an interval of less than 1 week, followed by (131)I therapy. The SPET images were reconstructed using the maximum likelihood expectation maximisation (ML-EM) method. All patients were hypothyroid at the time of each scan. (131)I WBS was performed 3-5 days after oral administration of the therapeutic dose. A total of 32 lesions [10 lymph node (LN), 15 lung, 6 bone, 1 muscle] were diagnosed as metastases, as confirmed by histopathology and/or other imaging modalities (X-ray, US, CT, MRI, bone, (201)Tl and (131)I scans). FDG-PET, (99m)Tc-MIBI SPET and post-therapeutic (131)I scintigraphy respectively revealed a total of 26 (81.3%), 20 (62.5%) and 22 (68.8%) lesions. These techniques respectively demonstrated nine (90.0%), eight (80.0%) and six (60.0%) LN metastases, and eleven (73.3%), seven (46.7%) and ten (66.7%) lung metastases. They each demonstrated five of the six bone metastases (83.3%). FDG-PET and (99m)Tc-MIBI SPET were positive in 17 (78.3%) and 14 (63.6%) of the 22 (131)I-positive lesions, respectively, and also in nine (90.0%) and six (60.0%) of the ten (131)I-negative lesions, respectively. Three of the five (131)I-positive and FDG-PET-negative lesions were miliary type lung metastases with a maximal nodular diameter of less than 10 mm. Comparison of FDG-PET with (99m)Tc-MIBI SPET revealed concordant results in 24 lesions, and discordant results in eight lesions (seven with positive FDG-PET alone and one with positive (99m)Tc-MIBI SPET alone).(a) even using whole-body SPET, FDG PET is superior to (99m)Tc-MIBI in terms of ability to detect metastases of DTC; (b) the higher sensitivity of FDG-PET compared with the previous studies could partly be due to increased serum TSH.

A 44-year-old euthyroid woman had two palpable nodules in the thyroid gland. 123I thyroid scintigraphy showed a hot nodule in the right lobe and a cold one in the left lobe. Total thyroidectomy was performed, and histopathologic examination revealed that both tumors contained papillary carcinoma. Thus, hot nodules on a thyroid scintigram with 123I do not necessarily preclude malignancy.

This study was done retrospectively to analyze the ultrasonographic (US) findings in thyroid scintigraphic hot areas (HA). Three-thousand, eight-hundred and thirty-nine consecutive patients who underwent 99mTc-pertechnetate (n = 3435) or 123I (n = 457) scintigraphy were analyzed. HA were regarded as present when the tracer concentration was greater than the remaining thyroid tissue, or when hemilobar uptake was observed. High-resolution US examinations were performed with a real-time electronic linear scanner with a 7.5 or 10 MHz transducer. One hundred and four (2.7%) were found to be scintigraphic HA (n = 120). US revealed a nodular lesion or well-demarcated thyroid tissue corresponding to the HA in 94 areas (78.4%, Category 1), an ill-defined region with different echogenicity in 13 areas (10.8%, Category 2), and no correlating lesion in 13 areas (10.8%, Category 3). These 104 patients included 43 with adenomatous goiter (59 areas), 33 with adenoma, 11 with Hashimoto's thyroiditis, 5 with primary thyroid cancer, 4 with euthyroid ophthalmic Graves' disease (EOG), 3 with hemilobar atrophy or hypogenesis, 2 with hemilobar agenesis, 2 with hypothyroidism with blocking-type TSH-receptor antibodies (TSHRAb), I with acute suppurative thyroiditis. Among the 59 adenomatous nodules and 33 adenomas, 51 (86.4%) and 32 (97.0%), respectively, belonged to Category 1. A solitary toxic nodule was significantly larger and occurs more often in older patients than in younger patients. On the other hand, all 17 patients with known autoimmune thyroid diseases including Hashimoto's thyroiditis, EOG and hypothyroidism with blocking TSHRAb belonged to Category 2 or 3. Possible underlying mechanisms are 1) hyperfunctioning tumors or nodules, 2) localized functioning thyroid tissue freed from autoimmune destruction, inflammation or tumor invasion, 3) congenital abnormality, 4) clusters of hyperactive follicular cells caused by long-term TSH and/or TSHRAb stimulation, 5) asymmetry, etc. Scintigraphic HA are observed in patients with various thyroid diseases and high-resolution US appears to be helpful clinically for the differential diagnosis of the above mentioned disorders.

Brain metastasis of differentiated thyroid cancer (DTC) often is detected during treatment of other remote lesions. We examined the prevalence, risk factors and treatment outcome of this disease encountered during nuclear medicine practice. Of the 167 patients with metastasis to lung or bone treated 1-14 times with radioactive iodine (RAI), 9 (5.4%) also had lesions in the brain. Five were males and 4 females, aged 49-84, out of the original population of 49 males and 118 females aged 10-84 (mean 54.7) years. Three of them underwent removal of their brain tumors, 5 received conventional external beam irradiation, and 2 had stereotactic radiosurgery with supervoltage X-ray. None of the brain lesions showed significant uptake of RAI despite demonstrable accumulation in most extracerebral lesions. Seven patients died 4-23 (mean 9.4) months after the discovery of cerebral metastasis, brain damage being the primary or at least a contributing cause. The 8th and 9th patients remained relatively well for more than 42 and 3 months, respectively, without any evidence of intracranial recurrence. Our results confirmed that the brain is a major site of secondary metastasis from DTC. No statistically significant demographic risk factor was detected. Any suspicious neurological symptoms in the course of RAI treatment warrant cerebral computed tomography. As for therapy, from our initial experience, radiosurgery seemed promising as an effective and less invasive alternative to surgical removal.

To develop a new method of radioimmunodetection for thyroid cancer, we tested the binding ability of a human antithyroglobulin monoclonal antibody, VB5, to primary culture of human thyroid cancer cells. VB5 was able to immunostain cytoplasmic thyroglobulin (Tg) in the acetone-fixed cancer cells when used in a labeled streptavidin-biotin method but not in a conventional indirect immunoperoxidase technique. The antibody was readily labeled with I-125 in the standard chloramin-T method, and showed specific binding to the antigen on cultured malignant thyrocytes displaceable with non-labeled VB5 or with excess Tg antigen. Although these initial results in vitro are encouraging, the observed low specific binding (about 1% at room temperature) to intact cells with a single monoclonal antibody seems insufficient to conduct any in vivo immunolocalization experiments in animals. To obtain more binding, we would need a cocktail of several monoclonal antibodies to different epitopes, and also fragmentation of antibody molecules to penetrate into cytoplasm.

We saw 24 thyrotoxic Graves' patients with normal thyroidal uptake of technetium-99m pertechnetate (99mTc) out of 201 untreated thyrotoxic Graves' patients seen over 4 years. The clinical and laboratory findings for these patients were studied and analysed. Thyroid uptake and scintigraphic examinations by means of 99mTc, TBII and TSab activity measurement clearly distinguished these patients from other thyrotoxic disorders (destruction-induced thyrotoxicosis and autonomously functioning thyroid lesions). Different from other disorders, these patients had not lower but normal thyroid uptake and also showed diffuse and discrete trapping into the enlarged glands. These patients had significantly smaller goiters, a lower serum thyroid hormone level, and lower TBII and TSab activity, when compared with other high 99mTc uptake groups with Graves' disease, and their condition could be easily controlled with small amounts of antithyroid drugs. Our study indicates that thyrotoxic Graves' disease with normal 99mTc uptake exists and 99mTc uptake study and TBII activity measurement is very useful for the diagnosis. The normal 99mTc uptake thyrotoxic Graves' patient might be early stage patients with general Graves' disease and their early discrimination from general Graves' patients is very advantageous for treatment and prognosis.