What Is Hypothyroidism?

Hypothyroidism is defined as a disorder of the endocrine system in which the thyroid gland is unable to produce enough thyroid hormone.

Hypothyroidism is one of the most known endocrine diseases of dogs. It happens in a condition when the thyroid gland delivers excessive amounts of T4 and T3 hormones into the bloodstream. Primary autoimmune thyroiditis occurs due to idiopathic thyroid gland atrophy or immune-mediated lymphocytic thyroiditis and is the most common presentation. Other rare reasons for canine hypothyroidism are congenital diseases due to the dysfunction of thyroid hormone biosynthesis blocked TSH secretion or thyroid gland abnormal development. 

These hormones are involved in virtually every metabolic activity within the body; hypothyroidism is associated with a definite pattern of clinical and laboratory manifestations attributable to low levels of thyroid hormones. Hormone assays are the only type useful in diagnosis; it requires many tests to come up with a firm conclusion. Indeed, the diagnosis should never be based on low T4 concentration alone.

Breeds Predisposed to Hypothyroidism

Certain breeds are more susceptible to developing hypothyroidism, including:

• Golden Retrievers
• Doberman Pinschers
• Irish Setters
• Boxers
• Dachshunds
• Cocker Spaniels

Causes Of Hypothyroidism in Dogs:

Hypothyroidism in dogs is what we can refer to as the state whereby the thyroid gland that is found in the neck does not secrete sufficient hormones. Such a deficiency can cause many health problems that can complicate the lives of people who suffer from the deficiency. The primary causes of hypothyroidism in dogs include: 

1. Autoimmune Thyroiditis (Lymphocytic Thyroiditis)

Hypothyroidism due to congenital defects is the most common cause of the disease in dogs. This is an autoimmune disease, the characteristic feature of which is the formation of antibodies against the thyroid gland in the body of the dog, which causes its destruction. Eventually, it impairs the gland’s capacity to synthesize thyroid hormones.

2. Idiopathic Thyroid Atrophy

In this condition, the thyroid gland undergoes progressive atrophy, and the gland conforms to the character of adipose tissue. The cause is not very well understood (which is why it is referred to as ‘idiopathic’) but it results in a decrease in the production of thyroid hormones by about 40-50%.

3. Congenital Hypothyroidism

Hypoplastic thyroid gland is very rare, but some dogs can be born with it. They both get inherited and if encountered they cause dwarfism, mental dullness, and other related developmental complications.

4. Neoplastic Destruction

Both benign and malignant tumors are possible in the thyroid gland as we have seen. Although the thyroid gland is not very frequently involved in tumor formation, if it occurs, it hampers the working of the gland and results in hypothyroidism.

5. Surgery or Radiotherapy

Hypothyroidism may also be secondary to thyroid surgery- thyroidectomy-, or neck radiotherapy for thyroid or other cancers. The above treatments can reduce or remove the manufacture of thyroid hormones.

6. Iodine Deficiency

These are, however, exceptional in the contemporary practice of veterinary medicine attributable to balanced commercial diets; lack of iodine is instrumental in hypothyroidism since iodine is used in the production of thyroid hormones.

7. Pituitary or Hypothalamic Disorders

The gland is controlled by the hypothalamus and pituitary gland that is found in the brain. Abnormalities of these glands, for example, tumor or injury, may hinder the signals to the thyroid gland, thus leading to low levels of hormones produced.

Symptoms Of Hypothyroidism in Dogs:

1. Weight Gain

The other major symptom of hypothyroidism is sudden, unintentional weight gain that has no apparent cause. The hypothyroid dog, on the other hand, may be able to eat regular or even reduced meal portions and still pack on weight because of the slow metabolism caused by the disease.

2. Lethargy and Fatigue

Dogs with hypothyroidism sit around and get easily exhausted. They may look lazy, and unfriendly as they often have no interest in playing and may look sleepy most of the time.

3. Hair Loss and Skin Issue

The common clinical sign includes hair loss, especially on the truncus, tail, and face. The coat may be lost, thinning, dry scaling, and ultimately, become brittle. Thickening, darkening of the skin, or formation of scaly, flaky skin (hyperkeratosis) are other complaints that can manifest in the skin.

4. Cold Intolerance

Dogs with hypothyroidism are also generally more susceptible to cold temperatures than normal dogs. They may look for warmth to lie down and they may feel shivering even under relatively high temperatures.

5. Behavioral Changes

As with most illnesses, some dogs might even get depressed, show little interest in their environment, or become more aggressive or anxious than usual.

6. Slow Heart Rate (Bradycardia)

A reduced pulse rate is another rare but equally serious sign of the condition. This may be picked by the vet during a normal physical examination of the dog.

7. Chronic Ear Infections

Hypothyroid-infected dogs may sometimes worsen the condition of the skin and ears leading to persistent ear infections.

8. Reproductive Issues

In female dogs’ hypothyroidism may affect the heart or the ability to get pregnant. In males, it may lead to impotence, low libido, and decreased sperm count among other symptoms.

9. Neurological Signs

Sometimes the neurological manifestations of hypothyroidism are seen which may include weakness, staggering, difficulty in control of hind limbs, or facial paralysis.

10. High Cholesterol Levels

Blood cholesterol is high in dogs with hypothyroidism, and this is a parameter that can be easily measured in the blood test.

 Treatment Of Hypothyroidism in Dogs:

Hypothyroidism is treated by using an oral drug known as levothyroxine. This medicine is a manmade version of the thyroid hormone which your dog is deficient in. In its treatment, hypothyroidism is a manageable condition although it is incurable.

Your dog will have to remain on thyroid replacement hormone for life. There are various doses of this pill, and your veterinarian will prescribe that which is right for your dog depending on the size. They will probably also wish to repeat blood tests in one month to check whether further modifications of the dose are needed.

When the disease is left untreated the dog risks living fewer years as almost every organ in the body is influenced by thyroid hormone and by metabolism. Thyroid hypothyroid dogs turn out to have high cholesterols, low immunity, slow heart rate, and neuromuscular disorders if left uncontrolled.

Some of these behavioral changes may be manifested in muscle weakness, swaying, and tilting of the head and may even develop seizures. Hypothyroidism is treatable and though not fatal, untreated hypothyroidism can reduce the quality of life of your dog.

CONCLUSION:

The best idea is to analyze the symptoms and consult the veterinarian as soon as possible. If hypothyroidism is left untreated then it can result in worse symptoms and health conditions. Severity can result in conditions like skin infections, heart problems such as slow rate, high cholesterol, any changes in the eye surface of dogs, and Myxedema coma which can be fatal too. The symptoms of hypothyroidism can develop gradually, or its signs may vary due to aging or other conditions. Early diagnosis and treatment with thyroid hormone replacement may help you manage conditions and improve your dog's quality of life.