Feline hyperthyroidism is the most common endocrine disorder in older cats and causes significant suffering when undiagnosed or undertreated.
Untreated hyperthyroidism causes progressive suffering — affected cats feel perpetually anxious, are ravenously hungry despite muscle wasting, experience chronic nausea, and develop secondary heart disease and hypertension. The condition is common, readily diagnosable on routine blood tests, and highly treatable. Because weight loss in aging cats is often misattributed to normal aging, hyperthyroidism is frequently diagnosed later than ideal. All cats over 8-10 years should have thyroid function assessed annually. Treatment restores quality of life dramatically in most cats within weeks.