Diabetes mellitus develops when the body cannot properly control blood glucose (sugar) levels. This usually happens because the body does not produce enough insulin or cannot use insulin effectively. Thyroid hormones increase the body’s energy use and can interfere with how insulin works. As a result, some cats with hyperthyroidism develop high blood glucose levels and may show clinical signs, or symptoms, such as increased thirst, increased urination, weight loss, and increased appetite.

Treating hyperthyroidism can sometimes improve diabetes. Once thyroid hormone levels return to normal, the body’s metabolism slows down and insulin may work more effectively again. In some cats, blood glucose levels become easier to control after treatment. Occasionally, diabetes may even resolve if hyperthyroidism was the main reason for the high blood sugar.

However, in other cats the diabetes remains even after the thyroid condition is treated. This happens because diabetes may already have been developing independently of the thyroid problem. For this reason, veterinarians usually monitor blood glucose levels when a cat with hyperthyroidism is being treated, especially if the cat is showing signs such as increased drinking or urination. If a cat has diabetes and is well controlled on medication, it may be suitable for treatment. Please chat to our team prior to referring a hyperthyroid cat with diabetes.