Mallery KF, Pollard RE, Hornof WJ, Feldman EC: Percutaneous ultrasonographically guided radiofrequency heat ablation for treatment of hyperthyroidism in cats. J Vet Intern Med 16:360, 2002.

Radiofrequency heat ablation of small tumors has been efficacious in humans. An insulated needle is guided into target tissue; a radiofrequency pulse applied, and heat formation at the needle tip results in coagulation necrosis. The purpose of this study was to evaluate efficacy of this treatment (Rx) modality for cats with naturally occurring hyperthyroidism. For inclusion in this study, each cat must have had: clinical signs of hyperthyroidism (polyphagia, weight loss, etc.), persistent increase in serum thyroxine concentration (sTT4) and not other condition that would contraindicate Rx. Nine cats met these criteria, and sTT4 ranged form 5.2-20.1 mcg/dl, (mean, 12.1 mcg/dl; reference range 1.1-3.9 mcg/dl). A solitary thyroid mass was identified via pertechnetate scintigraphy and cervical ultrasound in 4 cats (UNI). Two nodules were found in each of the ohter 5 cats (BI). Each cat was anesthetized and positioned in dorsal recumbency. With ultrasound guidance, an insulated 20-gauge catheter stylet was inserted into the thyroid mass and radiofrequency pulses applied for 30-60 seconds using an RF 2000 unit, Radiotherapeutics Redwood City, CA. In cats with bilateral disease, the larger mass was ablated. During ablation, treated tissue became hyperechoic secondary to nitrogen sublimation. Heat ablation was performed once on each of 3 thyroid nodules and twice on 1 nodule in the 4 UNI cats. Three of the 4 cats were euthyroid after the procedure, and hyperthyroidism recurred in all 3 cats: 4, 7 & 19 months post-Rx, respectively. One of these cats had a second ablation performed and remained euthyroid for 9 months. One of the 4 cats had reduction in sTT4 but did not become euthyroid. In the BI cats, heat ablation was performed once in 2 cats, twice in 2 cats, and three times in 1 cat. Each of these cats had heat ablation performed only on the larger nodule. Each of 2 cats became euthyroid after 1 heat ablation, for periods of 7 & 9 months, respectively. In each of the 2 cats that had 2 procedures performed, neither cat was euthyroid after the first procedure. One was euthyroid for 2 months after the second procedure, and 1 is euthyroid at the time this abstract was written (9 months post-Rx). The cat that had 3 procedures performed became euthyroid after the second and third procedure, for 5 months each time. Horner's syndrome developed in 2/9 cats, and resolved within 2 months in both cats. Unipolar radiofrequency heat ablation is feasible and effective as a short-term treatment for feline hyperthyroidism, but is not effective as a permanent treatment.