Article

Iodine Metabolism and Thyroid Disease in the Dog

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Thesis (doctoral)--Rijksuniversiteit te Utrecht.

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... 8 • 25 Other radioisotopes of iodine are less suitable because of inappropriate half-lives or photon energies, or an excessive absorbed radiation dose from particulate emissions. 8 · 15 • 25 Like stable iodine (1 27 1), radioactive iodine is actively concentrated or trapped by the thyroid gland, where it is incorporated into tyrosine residues of thyroglobulin in a process called organification. 8 • 15 • 25 Pertechnetate ion, with a size and charge similar to that of iodine, is also trapped by the thyroid gland. ...
... Hyperfunctional tumors causing hyperthyroidism appear as moderate to extensive areas of increased, usually uniform, tracer uptake (Fig. 9). [26][27][28] In some dogs, areas of normal to decreased tracer uptake are interspersed with hyperfunctioning areas. The intensity of the thyroid image is greater than that of the salivary glands on pertechnetate scans. ...
... (From Peterson ME, Becker DV: Radionuclide thyroid imaging in 135 cats with hyperthyroidism. Vet Radiol 25:[23][24][25][26][27] 1984; with permission.) ...
Article
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Nuclear medicine may have both diagnostic and therapeutic utility during the evaluation and management of thyroid disease. This article will focus on the use of radionuclide scintigraphy and radioactive iodine therapy in the diagnosis and treatment of thyroid disease in the dog and cat.
... In that study, rhTSH (100 mg IV, administered 24 h or 48 h before 123 I) also did not cause a significant change in thyroid RAIU. Earlier reports have suggested the potential of exogenous TSH to increase thyroid RAIU in dogs [26,27,28]. However, in these studies the effect of TSH stimulation on thyroid 131 I uptake was described in a small number of healthy and hypophysectomized dogs and no statistical analysis was performed. ...
... The significantly different effect of rhTSH on thyroid RAIU between euthyroid and hyperthyroid patients was an interesting finding. In a study of 55 dogs with thyroid tumors, dogs with evidence of autonomous hyperfunction of the goiter had an increased thyroidal iodine turn-over [28]. It is possible that a positive effect of rhTSH on tumor RAIU occurs sooner in hyperthyroid patients and was, therefore, not observed with our protocol (RAIU determination 8 h and 24 h after 123 I injection). ...
Article
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In humans, recombinant human thyrotropin (rhTSH) enhances radioactive iodine uptake (RAIU) in patients with differentiated thyroid cancer. No studies have been performed in veterinary medicine to optimize radioiodine treatment of thyroid cancer. The aim of this study was to evaluate the effect of rhTSH on the uptake of radioiodine-123 ((123)I) in dogs with thyroid tumors. Nine dogs with thyroid neoplasia were included in this prospective cross-over study. The dogs were divided in 2 groups. In one group, (123)I was administered for a baseline RAIU determination in week 1. In week 2 (after a washout period of 2 weeks), these dogs received rhTSH (100 μg IV) 24 h before (123)I injection. In the other group the order of the protocol was reversed. For each scan, the dogs received 37 MBq (1 mCi) of (123)I intravenously (IV) and planar scintigraphy was performed after 8 and 24 h for tumor RAIU calculation. Overall, rhTSH administration caused no statistically significant change on thyroid tumor RAIU at 8 h (p = 0.89) or at 24 h (p = 0.98). A significant positive correlation was found between the effect of rhTSH on tumor 8h-RAIU and rhTSH serum concentrations at 6 h (τ = 0.68; p = 0.03), at 12 h (τ = 0.68; p = 0.03) and at 24 h (τ = 0.78; p = 0.02) after rhTSH injection. This study suggests that IV administration of 100 μg rhTSH 24 h before (123)I has an inconsistent effect on thyroid tumor RAIU. Further studies are necessary to determine the best protocol of rhTSH administration to optimize thyroid tumor RAIU.
... These findings raise important issues regarding the optimal dosage, timing, and route of rhTSH administration when the goal is to increase thyroid RAIU, as earlier studies have shown that bTSH increases thyroid RAIU in healthy dogs and in dogs with secondary hypothyroidism. [66][67][68] Additional research therefore is warranted. ...
Article
Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.
... In most euthyroid humans (13) and dogs (1) maximal uptake values are reached between 24 and 48 hours, which was also the case in our healthy cats. In hyperthyroid humans (13) and dogs (7,11) the combination of a high thyroidal clearance and a rapid thyroidal turnover of iodine give a characteristic appearance to the thyroid radioiodine uptake curve. There is a rapid initial rise, followed by a decline due to the discharge of iodothyronines. ...
Article
Thyroidal radioiodine uptake was measured in 10 healthy domestic cats and in 20 hyperthyroid cats. Compared with those in the healthy cats, the uptake curves in the hyperthyroid cats were characterised by elevated uptake and rapid thyroidal iodine turnover. For diagnostic purpose uptake measurements at 4 hours after administration of the tracer were found to be preferable to measurements at 24 hours or later.
Thesis
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Het aantal publicaties over het gebruik van medische beeldvorming bij schildklieraandoeningen bij de hond is beperkt. Beschikbare studies rapporteren enkel het gebruik van echografie (US) en planaire scintigrafie in gevallen van schildkliertumoren. De toegenomen beschikbaarheid van andere beeldvorming- technieken, zoals Computed Tomography (CT) en Magnetic Resonance Imaging (MRI), maakt deze potentieel waardevol als bijkomstige testen in de soms moeilijke diagnose en bij het opstellen van een geschikt behandelingsprotocol voor schildklieraandoeningen bij de hond. Als voorbereidende studie werd de herhaalbaarheid van US metingen bepaald. Van verschillende metingen, gemeten door verschillende onderzoekers, hadden de hoogte- en volumemetingen de grootste herhaalbaarheid. De variatie binnen de verschillende onderzoekers was kleiner dan tussen de verschillende onderzoekers. De volgende kenmerken werden echografisch waargenomen in een populatie hypothyroIde honden: hypoechogeen en heterogeen parenchym, onregelmatige aflijning van het kapsel, ronde vorm van de schildklierlob op dwarsdoorsnede en verkleind schildklier volume. De vijf parameters gecombineerd, resulteerde in een sensitiviteit van 94% in de detectie van hypothyroidie. Een continue afname in volume van de schilkier werd opgemerkt na opstarten van de behandeling. US is een gevoelige en snelle test voor het opsporen van hypothyroidie bij de hond. Een volgend hoofdstuk handelt over de CT kenmerken van de normale schildklier bij de hond. De gemiddelde pre- en post-contrast attenuatie waarden waren zeer hoog voor weke delen. Na injectie van intraveneus contrast nam het schildklier volume toe. Alle schildklierlobben zagen er homogeen uit op zowel pre- als post-contrastbeelden. De ligging, de grootte en de vorm van de schildklierlobben werden beschreven. Bijschildklieren werden niet gezien en een isthmus werd slechts bij 1 op de 25 honden aangetroffen. Gezien de uitstekende zichtbaarheid en kenmerkende eigenschappen van de normale schildklier bij de hond besloten we dat het gebruik van CT voordelig zou kunnen zijn om het onderscheid te maken tussen nekmassa’s afkomstig van schildklierweefsel en nekmassa’s van andere oorsprong. CT heeft eveneens een potentiële rol bij het stageren van schildkliertumoren. Tot slot beschreven we de MRI kenmerken van de normale schildklier. De kenmerkende vorm, ligging en intensiteit vergeleken met de omliggende structuren maakten de schildklier duidelijk herkenbaar bij alle honden. Een isthmus werd slechts bij 1 op de 44 honden aangetroffen en bijschildklieren werden niet gezien. Gezien de uitstekende zichtbaarheid en kenmerkende eigenschappen van de schildklier op MRI werd er besloten dat MRI kan bijdragen tot de diagnose van diffuse schildklieraandoeningen, bij het onderscheiden van nekmassa’s van schildklieroorsprong en andere oorsprong, en bij de stagering en operatieplanning van schildkliertumoren.
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Seven dogs with thyroid gland carcinoma were treated with 131I and hormone suppressive therapy either alone (3 dogs) or in combination with surgery (3 dogs) or 137Cs teletherapy and chemotherapy (1 dog). Empirically chosen doses of 75 to 137 mCi of 131I were given orally (2 dogs) and intravenously (5 dogs). Adverse effects were limited to acute, transient bone marrow hypoplasia and pancytopenia. Nominal objective reduction in tumor volume or size and number of pulmonary metastases was observed in 4 dogs treated with 131I and thyroxine. Of these 4 dogs, 2 had stable disease for periods of 4 and 12 months while a third dog had stable disease for 27 months following two 131I treatments at 3 month intervals. The fourth dog had progressive disease. Two dogs with mediastinal metastases showed reduction in localization of 99mTc pertechnetate and radioiodine following 2 and 3 treatments using 131I. It appears that relatively high doses of 131I can be used safely for the treatment of canine thyroid tumors and that further investigation can be justified to define its efficacy.
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