Hypothyroidism in the Giant Schnauzer
The thyroid is a gland located at the front of the dogs neck with two lobes; one on either side of the trachea. The thyroid gland is under control of the pituitary gland at the base of the brain, which releases thyroid stimulating hormone (TSH), in order to regulate the amount of circulating thyroxine. Thyroxine is a hormone that normalises metabolism and is required at the correct levels by every cell in the body. When the thyroid gland isn’t producing enough thyroxine, it is under-active, and the amount of thyroxine available to the body is too low, leading to hypothyroidism. The dogs metabolism will slow down causing a number of different symptoms, when the metabolic rate slows down, virtually every organ in the body is affected. If there is a problem with the thyroid gland in the Giant Schnauzer it is most often under-active i.e HYPO-thyroid rather than over-active which is called HYPER-thyroid and is much more unusual. Hypothyroidism is usually caused by one of two diseases: autoimmune thyroiditis or idiopathic thyroid gland atrophy. Autoimmune thyroiditis is the most common cause of hypothyroidism and is thought to be a genetic immune-mediated disease. This means the immune system inherently decides that the thyroid is abnormal or foreign and starts to destroy it over time. It is unclear why this occurs, but when around 70% of the gland has been destroyed symptoms start to emerge. In idiopathic thyroid gland atrophy, normal thyroid tissue is replaced by fat tissue. This condition is also poorly understood. These two causes of hypothyroidism account for more than 95% of the cases in dogs. The other five percent are due to rare diseases, including cancer of the thyroid gland. From the last published joint Schnauzer breeds health survey, 8 out of 275 live dogs (3%) of those that took part in the survey reported Giant Schnauzers having hypothyroidism. One deceased dog reported hypothyroidism as the cause of death out of 90 (1%) deceased dogs, indicating that it is not generally a life threatening condition. The disease has variable onset, but tends to clinically manifest itself at 3 to 6 years of age. Young dogs may be clinically normal, only to become hypothyroid at a later date. It is currently not known how hypothyroidism is inherited in the Giant Schnauzer, and with idiopathic thyroid gland atrophy it is thought that environmental factors may also play a part, such as diet e.g. it is believed soy may destroy the thyroid, along with goitrogenic foods, such as spinach, broccoli, cauliflower, and possibly flaxseed, if given in large quantities. There are several articles which link hypothyroidism to fluoride and chlorine in our drinking water. Another factor is de-sexing a dog at too young an age. The sex hormones, especially oestrogen and testosterone, have a tremendous impact on the adrenals and subsequently on the thyroid. Research is also being done on the impact collars may have on the thyroid gland in terms of causing trauma. Further research is required to determine the mode of inheritance along with any possible environmental factors, however dogs with an increased level of thyroglobulin autoantibody (TgAA) are thought to have the inherited form of the disease, along with those where a family history is present. When the metabolic rate slows down, virtually every organ in the body is affected and symptoms may be quite vague. Most dogs with hypothyroidism have one or more of the following symptoms: Some dogs also have other abnormalities such as: Diagnosis can be made by a blood test, although may require a few specific blood levels to be checked and interpreted since a variety of factors can lead to lower thyroxine levels e.g. Illness not involving the thyroid gland (nonthyroidal illness) and certain medications, in addition large breed dogs and also senior dogs have lower levels of thyroxine. Therefore a definitive diagnosis requires careful attention to clinical signs and analysis of laboratory results. Tests that may confirm the diagnosis include combined measurement of the serum concentrations of total T4, free T4, and TSH. Blood cholesterol levels are also raised in 80% of dogs with hypothyroidism. And measurement of thyroglobulin autoantibody (TgAA) may also determine if the disease is inherited. Apart from breeding, Giant Schnauzers affected with hypothyroidism may otherwise live a perfectly normal life once the correct diagnosis and treatment is given and maintained. The disease itself isn’t life-threatening, and is relatively easy and inexpensive to treat. Prescription only thyroxine replacement is required on a daily basis for life, usually in the form of a tablet once or twice a day. It is advisable to monitor the blood thyroxine levels regularly, usually every 6-12 months under the direction of a vet. A few specific blood levels can be checked to determine thyroid health, and one test alone, such as just testing the circulating thyroxine levels (Total T4) may not be enough. Tests that may be used for health screeing and/or confirmation of the diagnosis include a full panel thyroid function test which measures the serum concentrations of total T4, free T4, and TSH (Thyroid stimulating hormone). Measurement of thyroglobulin autoantibody (TgAA) can also detect if a dog has the inherited version of the disease. TSH and TgAA may be raised many months or even years before clinical symptoms begin to develop, and as such can be used as a screening method before breeding a dog. Blood cholesterol levels are also raised in 80% of dogs with hypothyroidism. Blood tests can be carried out by your normal vet The Kennel Club currently does not publish results following thyroid function testing, however your vet should be able to provide a written report of the results. There is currently no requirement or recommendation in the UK for Giant Schnauzers to have their thyroid function tested before mating, however the breeder should be aware that it may occur, and be able to talk to you about hypothyroidism and what measures have been taken to avoid it. Should your dog develop hypothyrodism later in life, once detected it is generally fairly easy to manage and isn’t life threatening, although medication will be required indefinitely. Thyroid health can be assessed using a simple blood test to determine thyroid function prior to breeding, especially since an affected dog may be asymptomatic at the age of breeding. Thyroid function may also be a useful test if a dog has infertility problems or problems whelping/raising a litter, which can be associated with low thyroxine levels. A few specific blood levels can be checked to determine thyroid health, and one test alone, such as just testing the circulating thyroxine levels (Total T4) may not be enough. Tests that may be used for health screeing and/or confirmation of the diagnosis include a full panel thyroid function test which measures the serum concentrations of total T4, free T4, and TSH (Thyroid stimulating hormone). Measurement of thyroglobulin autoantibody (TgAA) can also detect if a dog has the inherited version of the disease. TSH and TgAA may be raised many months or even years before clinical symptoms begin to develop, and as such can be used as a screening method before breeding a dog. Blood cholesterol levels are also raised in 80% of dogs with hypothyroidism. Dogs affected with the inherited form of hypothyroidism (autoimmune thyroiditis) along with those having a family history, should not be used for breeding since their is no DNA test to determine which dogs are carriers, therefore risking producing affected offpsring. Blood tests can be carried out by your normal vet Currently there is no formal research being undertaken within the breed, although the AHT collect DNA samples from dogs affected with any conditions that may be inherited. Inform the breeder in order that they are aware for future reference and breeding decisions. In this way the incidence of health conditions can be monitored and any emerging problems identified. The purpose of the GSHF is to provide monies for research into inherited health problems in the Giant Schnauzer. All donations gratefully received.
What is Hypothyroidism?
What Causes Hypothyroidism?
Prevalence
Age of Onset
Mode of Inheritance
Signs & Symptoms
Diagnosis
Prognosis
Screening for Hypothyroidism
Where to go for a blood test
Publication of Results
Advice for Puppy Buyers
Advice for Breeders
Where to go for a blood test
Research into Hypothyroidism
If you Own an Affected Dog
Take part in the Joint Schnauzer Breeds Health Survey
If you own a dog diagnosed with hypothyroidism, please let us know by taking part in the Joint Schnauzer Breeds Health Surveys and/or contact the Breed Health Co-ordinator.Make a Donation to the GSHF