Hypothyroidism in dogs
The thyroid gland regulates the body’s metabolic rate. An overactive thyroid elevates the body’s metabolism (hyperthyroidism) whereas an underactive thyroid slows the metabolism (hypothyroidism).
What causes hypothyroidism in dogs?
The thyroid gland produces the hormone thyroxine, along with several other important thyroid hormones that are important in regulating your dog’s metabolism. Think of it like your dog’s thermostat. It is estimated that around 95% of hypothyroidism cases are caused by either lymphocytic thyroiditis or idiopathic thyroid gland atrophy. Of the two, lymphocytic thyroiditis is the most common and occurs when the immune system attacks the thyroid (immune-mediated disease). Experts believe that genetics play a significant role in this condition.
On the other hand, idiopathic thyroid gland atrophy occurs when the thyroid is replaced by fatty tissue. The reason this happens is not well understood.
Cancer and congenital defects of the thyroid are rarer causes of hypothyroidism.
Symptoms of hypothyroidism in dogs
The symptoms of hypothyroidism can vary greatly amongst dogs. Some breeds also appear to be more at risk of developing the disease. Medium to large-sized breeds are more prone to hypothyroidism, including the Cocker Spaniel, Miniature Schnauzer, Dachshund, Doberman Pinscher, Golden Retriever, Airedale Terrier, and Irish Setter. Any breed can however develop the disease.
Common symptoms include:
- Weigh gain without an increase in appetite
- Lack of wish to exercise
- Gets cold easily
- High blood cholesterol
- Mental dullness
- Change in coat (hair thinning because of increased shedding)
- Thickening of the skin
- Slow heart rate
- Infertility in intact dogs
Some dogs also experience abnormal function of the nerves, thickening of the facial skin, fat deposits in the corneas of the eyes or dry eye due to lack of proper tear production.
How your vet will diagnose hypothyroidism in your dog
A total thyroxin (TT4) level screening test is common. According to VCA Hospitals (in an article by Krista Williams, BSc, DVM and Ernest Ward, DVM) “A low level of total thyroxin, along with the presence of clinical signs is suggestive of hypothyroidism … a definitive diagnosis is made by performing a free T4 by equilibrium dialysis (free T4 by ED) or a thyroid panel that assesses the levels of multiple forms of thyroxin. If this test is low, then your dog has hypothyroidism.”
How your vet will treat the disease
Although hypothyroidism is not curable, it is treatable. Your veterinarian will likely give your dog an oral hormone replacement medication, for the rest of its life. It is important to realise that this is not a death sentence nor is it a ‘difficult to administer’ drug. The medication is often inexpensive and the outcome favourable.
Many diseases mimic hypothyroidism. It is therefore important to work with your vet to confirm the disease. Your vet will monitor your dog and change the dosage from time to time.