Hyperthyroidism is the most common hormonal disease in aging cats. It is diagnosed in approximately 10% of cats over 10 years of age. The thyroid gland produces excess thyroid hormone (T4), which accelerates metabolism and strains many organs — especially the heart and kidneys. Left untreated, the disease leads to serious complications, but with proper treatment the prognosis is good.
Symptoms
The most common symptoms are weight loss despite good appetite, increased drinking and urination, vomiting, diarrhea, hyperactivity or restlessness, poor coat and rapid heart rate. Some cats also show wasting, muscle loss and behavioral changes. Symptoms usually develop slowly, and owners may mistake them for normal age-related changes.
Diagnosis
Diagnosis is based on a blood test measuring thyroid hormone T4. An elevated T4 value together with typical symptoms confirms the diagnosis. Sometimes T4 can be normal even when the disease is present — then free T4 (fT4) is measured. During clinical examination, the vet can feel an enlarged thyroid gland in the neck area. At the same time, the heart, blood pressure and kidney values are checked.
Complications
Untreated hyperthyroidism can cause heart enlargement (hypertrophic cardiomyopathy), high blood pressure, retinal detachment and vision problems. There is also an important connection to kidney disease: hyperthyroidism increases blood flow to the kidneys, which can mask underlying kidney failure. When thyroid function is corrected, hidden kidney disease may be revealed. That is why kidney values are monitored closely during treatment.
Treatment Options
There are four treatment options: 1) Daily medication (methimazole/Felimazole) — the most common option, affordable but lifelong. 2) Surgery (thyroidectomy) — removal of the thyroid gland, a curative treatment. 3) Radioactive iodine therapy (I-131) — the gold standard, one treatment cures over 95% of cases but requires a specialized clinic. 4) Prescription diet (Hill's y/d) — iodine-restricted food, suitable for cats with mild symptoms. At our clinic, we help you choose the best treatment for your cat's situation.