Thyroid problems in pets – hypo- and hyperthyroidism

The thyroid gland plays an important role in metabolism through the production of the hormones T4 and T3. When these hormones are present at too low or too high levels, this leads to serious disruptions in the body. In dogs, hypothyroidism (an underactive thyroid) is most common, while in cats, hyperthyroidism (an overactive thyroid) often occurs.

In this article, we discuss the causes, symptoms, diagnosis, and treatment of thyroid problems in pets.

What are thyroid problems?

The thyroid gland produces the hormones T4 and T3, which have a major influence on metabolism, growth, and energy balance. A disruption can lead to hypothyroidism (deficiency) or hyperthyroidism (excess).

Hypothyroidism in dogs

Causes

Hypothyroidism in dogs is usually caused by an autoimmune reaction that affects the thyroid tissue (lymphocytic thyroiditis).

Symptoms

• Lethargy and reduced activity
• Weight gain despite normal feeding
• Skin and coat problems (hair loss, flaking, thickened skin)
• Cold intolerance
• Slow heart rate

Diagnosis

The diagnosis is made through blood testing:

• Decreased total T4
• Elevated TSH (thyroid-stimulating hormone)
• Sometimes additional tests such as scintigraphy or a TSH stimulation test

Treatment

Treatment consists of lifelong administration of synthetic thyroid hormone (levothyroxine). After starting therapy, blood values are checked regularly and the dose is adjusted.

Hyperthyroidism in cats

Causes

Hyperthyroidism in cats is usually caused by a benign enlargement of the thyroid gland (adenoma). Rarely, it is due to a malignant tumor (carcinoma).

Symptoms

• Weight loss despite a good appetite
• Increased thirst and urination
• Restlessness and hyperactivity
• Vomiting and diarrhea
• Rapid heart rate and sometimes cardiac arrhythmias
• Poor coat condition

Diagnosis

The diagnosis is made through:

• Blood testing: elevated total T4
• Sometimes additional ultrasound or scintigraphy to image the thyroid gland

Treatment

Possible treatments include:

• Medication (such as methimazole or carbimazole) to suppress hormone production
• Surgical removal of the affected thyroid gland (thyroidectomy)
• Radioactive iodine therapy (most effective, destroys overactive tumoral thyroid tissue)
• Diet with an extremely low iodine content (as a temporary or supplementary therapy)

Recovery and prognosis

In dogs with hypothyroidism, the prognosis is excellent with lifelong hormone therapy. In cats with hyperthyroidism, the prognosis is good, especially with timely treatment. Complications can arise from heart problems or kidney problems that have been worsened by the hyperthyroidism.

Want to know more?

Read more about our services in internal medicine and endocrinology. Our specialized veterinarians at Nesto have extensive experience in diagnosing and treating thyroid problems and offer individual treatment plans for dogs and cats.

Frequently asked questions (FAQ)

What is the difference between hypothyroidism and hyperthyroidism?

Hypothyroidism is a deficiency of thyroid hormone (usually in dogs), hyperthyroidism is an excess (usually in cats).

What symptoms will I see in my pet?

With hypothyroidism, mainly lethargy and weight gain; with hyperthyroidism, weight loss and hyperactivity.

How is the diagnosis made?

Through blood testing (T4, TSH) and sometimes imaging such as ultrasound or scintigraphy.

Can thyroid disease be cured?

Hypothyroidism cannot be cured and requires lifelong hormone therapy. Hyperthyroidism can often be treated definitively, for example with radioactive iodine.

What is the prognosis?

With proper treatment, most dogs and cats have an excellent quality of life.