In clinically hyperthyroid cats, is I-131 treatment superior to thyroidectomy in normalising serum T4 level?

PICO question In clinically hyperthyroid cats, is iodine-131 (I-131) treatment superior to unilateral or bilateral thyroidectomy in normalising serum thyroxine (T4) levels?   Clinical bottom line Category of research question Treatment. The number and type of study designs reviewed 35 papers were critically reviewed. These were mostly retrospective studies with a small proportion of prospective cohort studies. Strength of evidence Moderate. Outcomes reported More papers were available evaluating the effect of radioiodine therapy on T4 levels compared to thyroidectomy. Long-term follow-up of T4 is a relatively new component of study designs. Most papers suggested between 40–87% cats had normal T4 6 months after treatment. 19–47% cats receiving unilateral or bilateral thyroidectomy, and 100% cats receiving radioiodine therapy were in long-term remission in one study. Conclusion In view of the of evidence and outcomes from the studies, there is moderate evidence that I-131 treatment is superior to unilateral or bilateral thyroidectomy.   How to apply this evidence in practice The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources. Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.