Cross-sectional analysis of 152 hyperthyroid cats presented for radioactive iodine therapy in South Korea.

Introduction: Feline hyperthyroidism is one of the most common endocrinopathies in cats; however, its epidemiological characteristics remain poorly understood in South Korea. Although radioactive iodine therapy (RAIT) is a definitive treatment, studies focusing specifically on cats with hyperthyroidism undergoing RAIT are limited. Methods: Medical records of 152 cats with hyperthyroidism presented for RAIT were retrospectively reviewed to describe their epidemiological and clinical features. Results: The median age at diagnosis was 12 years, and 30.3% of the cats were diagnosed incidentally. RAIT was usually performed soon after diagnosis, with a median disease duration of 5 months; only 4.6% of cats had a disease duration >2 years. Unilateral thyroid disease was the predominant pattern (50.7%), and severe hyperthyroidism (total thyroxine ≥19.4 μg/dl) was observed in 10.5% of cats. Only 40.1% of cats underwent RAIT following the veterinarian's recommendation, whereas 59.9% of owners sought RAIT independently. Human-licensed or generic methimazole was used more frequently than veterinary-licensed methimazole (84.0 vs. 18.1%). Pruritus occurred more frequently with human-licensed or generic methimazole than with veterinary-licensed methimazole ( Conclusions: This is the first study to characterize cats with hyperthyroidism that were presented for RAIT in South Korea. Key findings included an owner-driven pattern of RAIT selection, early use of definitive therapy despite a relatively late diagnosis, predominant use of non-veterinary methimazole formulations, and a higher frequency of pruritus as an adverse effect. These findings contribute to the epidemiological understanding of feline hyperthyroidism and may inform clinical decision-making in South Korea.