Use of percutaneous ethanol injection for treatment of bilateral hyperplastic thyroid nodules in cats

Objective - To determine the efficacy and safety of percutaneous ethanol injection (PEI) for the treatment of hyperthyroidism caused by bilateral hyperplastic thyroid nodules in cats. Design - Prospective study. Animals - 7 cats. Procedure - Hyperthyroidism was diagnosed on the basis of clinical signs and increased serum total thyroxine (Π₄) concentrations. The presence of 2 cervical thyroid nodules was confirmed by use of ultrasonography and technetium Tc 99m albumin thyroid scans. After the death of 1 cat that received PEI in both thyroid nodules at the same time, the protocol was changed to injecting ethanol into 1 nodule at a time, with at least 1 month between injections. Clinical signs, serum Π₄ concentrations, serum ionized calcium concentrations, laryngeal function, findings on ultrasonographic examinations of the ventral cervical region, and results of thyroid scans were monitored. Results - Serum Π₄ concentrations transiently decreased in all 6 cats (into the reference range in 5 of 6 cats) within 4 days of the first staged ethanol injection. Each subsequent injection resulted in a transient decrease in serum Π₄ concentration. The longest period of euthyroidism was 27 weeks. Adverse effects included Homer's syndrome, dysphonia, and laryngeal paralysis. One cat died of unrelated causes. One cat underwent bilateral thyroidectomy, 2 cats were treated with methimazole, and 2 cats that had increased serum Π₄ concentrations were not treated further, because they remained clinically normal. Conclusions and Clinical Relevance - Percutaneous ethanol ablation of bilateral thyroid nodules as a treatment for cats with hyperthyroidism is not recommended. This treatment is not as efficacious as the medical and surgical treatments presently used.