What is canine hypothyroidism?

Hypothyroidism is a relatively common condition in dogs and is usually relatively easy to treat. The condition results from a lack of production of thyroid hormone from the thyroid gland in the neck. Given that the thyroid hormones play a major role in controlling metabolism (as well as some other important jobs), a lack of these hormones causes the metabolism to slow. In contrast, when too much of these hormones are produced by the thyroid gland then the metabolism runs faster than it should – this is the case with the condition hyperthyroidism which tends to affect older dogs.

What causes canine hypothyroidism?

In approximately 95% of cases hypothyroidism is caused by direct destruction of the thyroid gland, usually due to it being inappropriately targeted by the dog’s immune system. It is more common in middle-aged dogs and medium to large-sized breeds such as Golden Retrievers, Labradors, Dobermans, Boxers and Irish Setters, although any breed can be affected.

What are the symptoms of canine hypothyroidism?

The symptoms are typically vague and develop gradually, but usually include:

• Lethargy and mental dullness
• Weight gain without a change in appetite
• Dry dull coat with increased shedding
• Patchy fur loss
• ‘Rat tail’ due to fur loss on the tail
• Changes in the skin including pigmentation, flaking and recurrent infections
• Thickening of the skin around the face, leading to a ‘sad’ expression
• Intolerance to cold – they may seek out warm places
• Reproductive disturbances in entire males

How is canine hypothyroidism diagnosed?

If your vet is concerned about the possibility of hypothyroidism in your dog they will suggest running some blood tests. We can measure the level of thyroid hormone (T4) in the blood to see if it is lower than it should be. However, the T4 level can also be affected by a number of other conditions not related to hypothyroidism, so it is important to see the big picture and not diagnose this condition on the basis of a low thyroid level alone. Your vet may therefore recommend some additional blood tests to confirm that a low T4 is genuinely due to hypothyroidism rather than a non-thyroidal illness.

How can canine hypothyroidism be treated?

Hypothyroidism is normally relatively easy to treat with synthetic thyroid hormones given as a daily tablet. The dosage varies between dogs, so all are given an initial dose but this may need to be adjusted according to blood tests that monitor the thyroid hormone level. Given that the destruction of the thyroid gland can worsen over time, it is important that the hormone level is monitored and the drug dosage increased as needed. The treatment is life-long but most symptoms improve within a few weeks or months. When the condition is well managed, dogs have an excellent prognosis and normal life expectancy.