While hyperthyroidism is common in elderly cats, hypothyroidism is rare but causes significant welfare problems when it occurs, particularly post-treatment.
Iatrogenic hypothyroidism is an important welfare complication of hyperthyroid treatment. Over-treatment causing insufficient thyroid hormone causes lethargy, cold sensitivity, and weight gain. Post-treatment monitoring ensures thyroid levels are maintained in the normal range, preventing both untreated hyperthyroidism and iatrogenic hypothyroidism.