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Canine hypothyroidism

The thyroid is a small gland located in the neck. It produces hormones that regulate the speed at which the body functions. In hypothyroidism, this gland no longer produces enough hormones: everything slows down. The dog becomes limp, gains...

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

The thyroid is a small gland located in the neck. It produces hormones that regulate the speed at which the body functions.

In hypothyroidism, this gland no longer produces enough hormones: everything slows down. The dog becomes limp, gains weight without eating more and its coat deteriorates.

It is the most common hormonal disease in adult dogs. It sets in slowly, often over several months, and owners readily blame it on age.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Fatigue Reduction Hair loss Dull coat Scabs and skin lesions Itching Weight gain Thickened or darkened skin Heat intolerance Behaviour change

Decreased energy: the dog sleeps more, gets tired quickly when walking, seeks less play.

Weight gain even though the ration has not changed.

Seeking warmth, unusual chilliness.

Dry, dull, brittle hair, which grows back poorly after shearing.

Symmetrical hair loss on both sides of the body, often on the flanks, tail and back of the thighs, usually without itching at first.

Thickened, darker skin, sometimes oily with dandruff.

Skin or ear infections that keep coming back and are itchy.

In some dogs, the facial expression appears frozen, the eyelids droop slightly.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

In the vast majority of cases, the thyroid gland is gradually destroyed by the body itself (immune reaction directed against the thyroid) or replaced by fatty tissue.

Much more rarely, the defect is located not in the gland but in the area of the brain which gives it its orders.

A form present from birth exists in puppies but remains exceptional.

Certain medications and certain general illnesses temporarily lower thyroid hormones without it being true hypothyroidism: this is one of the reasons why the veterinarian never relies on a single dosage.

Adult to mature age: the disease most often appears between four and ten years of age.

Medium to large breeds more commonly affected include the Golden Retriever, Labrador, Irish Setter, Doberman, Boxer and Poodle.

Previous sterilization is sometimes found in the statistics, without it explaining the disease alone.

Very small breeds and very young dogs are rarely affected.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The diagnosis cannot be made based on visible signs alone, because fatigue, weight gain and skin problems exist in many other diseases.

The veterinarian performs a complete examination, palpates the skin and neck, then orders a blood test.

This analysis includes a general assessment (count, kidneys, liver, blood sugars and fats) and the dosage of thyroid hormones. High cholesterol and moderate anemia are common clues.

Depending on the results, additional dosages are requested to distinguish true hypothyroidism from a temporary decrease linked to another illness or ongoing treatment.

It is important to report all medications and supplements given to the dog: some distort interpretation.

Treatment

Treatment consists of replacing the missing hormone with a synthetic thyroid hormone, given by mouth, every day, for life.

The doses and rhythm are set by the veterinarian for each dog: they are never copied from one animal to another.

Blood checks are scheduled after the start of treatment, then regularly, to adjust the quantity as accurately as possible. An excess of the hormone is as harmful as a deficiency.

Energy and appetite often return within a few weeks; the coat takes several months to rebuild.

Associated skin or ear infections are treated in parallel, otherwise the dog continues to scratch even though the hormone has already been corrected.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

There is no way to prevent the onset of the disease.

Dogs from affected bloodlines should not be chosen for breeding.

A blood test during annual visits, especially from middle age, allows the disease to be identified before it affects quality of life.

Monitoring weight at home at regular intervals helps spot unexplained weight gain.

Possible complications

Repeated skin infections and ear infections until the hormone is corrected.

Sustainably high level of fats in the blood.

Nervous disorders in old or severe forms: weakness of the limbs, damage to the facial nerves, difficulty with balance.

Decreased fertility in breeding female dogs and males.

In rare and advanced cases, a state of extreme weakness with a drop in body temperature which constitutes an emergency.

When to see a veterinarian

Your dog is gaining weight even though his ration has not changed.

He is tired, less playful, seeks warmth and sleeps a lot more than before.

Their hair becomes dull, falls out on both sides of the body symmetrically or does not grow back after shearing.

It continues with ear infections or skin infections despite treatment.

He becomes very depressed, cold to the touch and no longer gets up: consult urgently.

Prognosis

The prognosis is very good. With daily treatment and regular check-ups, most dogs return to a perfectly normal life and an unchanged life expectancy.

Relapses of signs almost always correspond to poorly adjusted or irregular treatment rather than a worsening of the disease.

Frequently asked questions

My dog is gaining weight and sleeping a lot: is it necessarily the thyroid?

No. A diet that is too rich, lack of exercise, osteoarthritis or other hormonal diseases give the same picture. Only a blood test, interpreted with the clinical examination, can make a decision.

Is the treatment lifelong?

Yes, in almost all cases. It replaces a hormone that the gland no longer produces; stopping it causes the signs to return within a few weeks.

Can hypothyroidism be treated with diet?

No. No food or supplement replaces the missing hormone. A suitable diet, on the other hand, helps to manage weight while the treatment takes effect.

How long before the hair grows back?

Energy often returns within a few weeks, but the coat takes several months. This is normal and is not a sign of treatment failure.