Hypothyroidism in Dogs

Claire Dunling

Hypothyroidism in dogs is an unfortunate illness. However, with your vet’s advice and a good understanding of the condition, it can be managed effectively and your dog can still lead a full and happy life.

Quite simply hypo as a prefix means “under” and “thryoidism” refers to thyroid activity. So if a dog is hypothyroid, their thyroid gland is underperforming.

The two most common diseases that cause or create this the condition are lymphocytic thyroiditis idiopathic and thyroid gland atrophy. The former is the most common cause of dog hypothyroidism and is thought to be an immune-mediated disease. Idiopathic thyroid gland atrophy is less common and as a result, less well understood. Together these cause 95% of cases of hypothyroidism. The other five per cent are due to far rarer instances eg. cancer of the thyroid gland.

What are the common symptoms of hypothyroidism?

Some dogs also have additional less common symptoms:

How is hypothyroidism in dogs diagnosed?

If you vet suspects hypothyroidism they’ll run a blood test on your dog to measure the level of the main thyroid hormone,  known as a “T4 level test”. If the blood test results show a low level of thyroid hormone and the dog is displaying the symptoms, this may indicate to the vet that the dog is suffering from hypothyroidism. However, the T4 level test can be misleading, because some dogs that are not hypothyroid may have abnormally low levels – which could be caused by another disease or even any current medication. So do not be surprised if they run further test to be certain.

Don't be alarmed if your vet runs more tests after the T4 blood sample. The test is a good indicator but not 100% conclusive proof of hypothyroidism
John Campbell, Head Vet of Pet Drugs Online

What treatments are there for dog hypothyroidism?

Hypothyroidism is treated with thyroid replacement hormone, usually given orally. As hypothyroidism is not a curable disease but can only be managed, your dog will need these drugs for the rest of their lives. The vet will prescribe an initial dose based on your dog’s weight, then after about a month of treatment, they will carry out further tests to refine the ongoing dosage.

Typically your vet will need to check these levels every 6-12 months in order to ensure that the dog is getting the right dosage. Within a few months, your dog’s energy levels and behaviour, hair growth and overall skin should all show improvement. Once their energy levels are back up, moderate exercise and a healthy diet (of course) will get their weight down.

You will need to be rigorous and never miss a dose or a check-up, but if you do then in return you’ll get your old dog back. So it is a small price to pay!

This post is an opinion and should only be used as a guide. You should discuss any change to your pet’s care or lifestyle thoroughly with your vet before starting any program or treatment.

If in doubt contact your veterinary practice

And always keep your vet's phone number handy - just in case!