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 (p = 0.047). All cats were housed indoors. The regional distribution of cases differed from the reported national distribution of owned cats (p = 0.016). No cats originated from Jeju-do, which differed significantly from the mainland regions (p = 0.0004). Longer disease duration was associated with more advanced disease, including higher thyroid hormone levels and scintigraphic activity, increased bilateral involvement, and a higher rate of refractory response to antithyroid drugs (all p ≤ 0.001).

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.