HYPOTHYROIDISM EPIDEMIC IN DOGS!

Not doubt you’ve seen headlines like this. No doubt you’ve read the articles which blame vaccines, or dog food, or inbreeding. But is there an epidemic of hypothyroidism, and if so, what is the real cause?

DOES YOUR DOG HAVE HYPOTHYROIDISM?

Hypothyroidism is usually seen in middle aged dogs. As the thyroid gland controls the metabolic rate of the whole body a reduction in how well the gland works will have a wide range of symptoms. The most common are weight gain, lethargy, and  poor skin and coat. Recurrent infections, exercise intolerance, cold intolerance, and mental dullness can also be seen. Unfortunately these symptoms are not unique to hypothyroidism and can be seen in other diseases common to middle aged dogs. 

If your vet suspects hypothyroidism she will take a blood sample. The usual first test is to look at free T4 and TSH levels in the blood. A classic hypothyroid case will have low T4 and high TSH. This test is very sensitive and will pick up most hypothyroid cases….but it isn’t very specific and will pick up lots of non hypothyroid cases too. Many illnesses can cause the free T4 levels to be low when sampled, and the level fluctuates through the day. A vet must never diagnose hypothyroidism just on a blood sample, but must consider the whole clinical picture. A few dogs have classic symptoms of hypothyroidism but relatively normal blood values, again the vet must decide whether to trial treatment. Treatment is cheap and safe (it just replaces the missing hormone) so in cases where the blood tests are inconclusive vets will often try a month of treatment.

Additional tests are available including T3, and thyroid antibodies. T3 is the active form of thyroid hormone but little circulates in the blood (most is in the cells) and free blood values do not correlate well with clinical signs. Thyroid antibodies make the autoimmune form of thyroid destruction very likely, but a lack of antibodies doesn’t mean thyroid damage hasn’t taken place.

VACCINATION CAUSES HYPOTHYROIDISM IN DOGS!

Hypothyroidism is the most common endocrine disease of dogs, affecting between 2 and 6 dogs per 1000 (so the risk of any dog developing hypothyroidism in it’s life is 0.2-0.6%). Almost 80% of puppies, and nearly 70% of adult dogs receive vaccinations so there is a good chance hypothyroid dogs will also have been vaccinated…but this doesn’t mean that vaccines cause hypothyroidism. Because around 50% of thyroid cases are caused by the body’s immune system attacking the thyroid gland is has been suggested that vaccines trigger the immune system into an attack. To date though no studies have proven that this happens. It has also been suggested that the immune system starts to go wrong after infection, but again a definitive cause and effect has not been shown. Autoimmune diseases seem to be on the rise generally and a theory often discussed is that because of good hygiene, vaccinations, and parasite control the juvenile immune system isn’t correctly primed. One of the few things we do know is that there is a genetic component to hypothyroidism as it has been shown to run in family lines and be more common in some breeds than others. Studies on gender and neutering status suggest neutered females may be at higher risk. There is a feeling amongst vets that hypothyroidism may be on the rise, but increased pet owner and vet awareness, and the increase in ‘wellness’ blood tests for older pets may simply mean we are detecting more cases.

HYPOTHYROIDISM CAUSES AGGRESSIVE BEHAVIOUR IN DOGS!

Hypothyroidism is increasingly blamed for aggression in dogs, but again scientific papers really do not back this up. There are a few case reports but in most cases changes in behaviour can be explained by other factors. There is no doubt that hypothyroid dogs feel rubbish and many have skin infections. If the dog is forced out for a walk, away from his warm place, or molested by children he may feel forced to act in an aggressive way. As hypothyroidism usually affects middle aged dogs other health problems may contribute to the feelings of grumpiness or difficulty in coping with their world; arthritis, dental pain, hearing problems, vision problems etc.

Changes in behaviour in middle aged dogs should always prompt a trip to the vet to rule out health problems.

So…is there an epidemic of hypothyroidism? Maybe not. Is there a clear link to vaccination? No. Does hypothyroidism cause aggression? Usually no, but it can make dogs miserable and grumpy. Can a single blood test (even an expensive one from America) tell me if my dog has a thyroid problem? No. If you have any concerns about your dog’s health book a check up with your vet. And remember we’re available to help with acupuncture, herbal medicines, and behaviour assessments!