My cat George was always hungry. When he was young we called him Fat George. As he aged he became thinner and thinner. When he was 12 years old I noticed that his activity levels as well as his appetite were reaching record levels.
At first I thought he'd reverted to kittenhood but soon found that one of the thyroid glands on the lower part of his neck was as big as a lima bean. A blood test confirmed the diagnosis of hyperthyroidism.
I surgically removed the gland and he was normal for a few years before I noticed his appetite rocket again. This time I medicated him with an anti-thyroid drug that worked very well. I gave him a tablet twice a day until he became too cunning for me. I switched to applying a medicated gel to the inside of his ears and won the battle.
Like most old cats George eventually developed kidney disease. I had to ease off the antithyroid medication and nurse his old kidneys along.
This candid shot is of George not long before he died. Even when his kidneys were about to collapse his overactive thyroid drove his appetite to spectacular heights (depths?!)