Hyperthyroidism is the most common hormonal disorder in older cats, causing significant suffering when untreated and responding well to multiple treatment options when diagnosed.
Feline hyperthyroidism is a highly treatable condition whose welfare impact is entirely determined by whether it is diagnosed and managed. An undiagnosed hyperthyroid cat lives in a state of chronic physiological dysregulation: the elevated thyroid hormone causes constant hypermetabolism — cats burn energy faster than they can consume it, lose muscle mass despite ravenous eating, and experience cardiovascular strain from sustained elevated heart rate. Secondary hypertension can cause sudden blindness from retinal detachment and further cardiac damage. The condition is easy to diagnose with a routine blood test and straightforward to manage. Radioactive iodine treatment, now widely available, permanently resolves hyperthyroidism without daily medication and is curative for most cats. Owners who dismiss signs including weight loss and increased vocalization in older cats as normal aging are missing a treatable welfare problem.