Hypothyroidism

Hypothyroidism in the Giant Schnauzer

Info

What is Hypothyroidism?

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.

What Causes Hypothyroidism?

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.

Prevalence

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.

Age of Onset

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.

Mode of Inheritance

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.

Signs & Symptoms

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:

  • Weight gain without an increase in appetite
  • Lethargy and lack of desire to exercise
  • Cold intolerance (gets cold easily)
  • Dry, dull hair with excessive shedding and flaking
  • Very thin to nearly bald coat, usually on the tail and body
  • Increased dark pigmentation in the skin
  • Increased susceptibility and occurrence of skin and ear infections
  • Failure to re-grow hair after clipping or shaving
  • High blood cholesterol
  • Slow heart rate
  • Behavioral changes such as aggression, fear, anxiety, OCD type behaviors

Some dogs also have other abnormalities such as:

  • Thickening of the facial skin so they have a “tragic facial expression”
  • Abnormal function of nerves causing non-painful lameness, dragging of feet, lack of coordination, and a head tilt
  • Loss of libido and infertility in intact males
  • Lack of seasons, infertility, and abortion in females
  • Fat deposits in the corneas of the eyes
  • Dry eye (Keratoconjunctivitis sicca) due to lack of proper tear production

Diagnosis

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.

Prognosis

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.

Health Screening

Screening for Hypothyroidism

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.

Where to go for a blood test

Blood tests can be carried out by your normal vet

Publication of Results

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.

Buyer Advice

Advice for Puppy Buyers

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.

 

Breeder Advice

Advice for Breeders

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.

Where to go for a blood test

Blood tests can be carried out by your normal vet

How You Can Help

Research into Hypothyroidism

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.

If you Own an Affected Dog

Inform the breeder, and also breeder of the sire where possible in order that the breeder is aware for future reference and breeding decisions.

Take part in the Joint Schnauzer Breeds Health Survey

Joint Schnauzer Health SurveyIf 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.

In this way the incidence of health conditions can be monitored and any emerging problems identified.

 

Make a Donation to the GSHF

The purpose of the GSHF is to provide monies for research into inherited health problems in the Giant Schnauzer. All donations gratefully received.

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