Hey there, pet parents. Is your middle-aged dog gaining weight despite not eating more, and seeming sluggish and lazy? Are they developing skin problems and a thinning coat? If this sounds familiar, you could be looking at one of the most common hormonal diseases in dogs: Hypothyroidism. Let's break down this condition.
What is Hypothyroidism?
"Hypo" means low or underactive, so hypothyroidism is a condition where the thyroid gland is not producing enough thyroid hormone. The thyroid gland is a small, butterfly-shaped gland in the neck that acts as the body's thermostat. Thyroid hormone controls the body's metabolism.
When there isn't enough thyroid hormone, the entire metabolism slows down. This affects almost every organ system in the body, which is why the signs of hypothyroidism can be so varied.
What Causes Hypothyroidism?
In over 95% of cases, hypothyroidism is caused by the dog's own immune system attacking and destroying the thyroid gland. This is called lymphocytic thyroiditis. We don't know why the immune system does this, but it is known to be a hereditary condition in certain breeds.
Breeds that are predisposed include:
- •Golden Retrievers
- •Doberman Pinschers
- •Irish Setters
- •Cocker Spaniels
- •Airedale Terriers
The disease usually becomes apparent in middle-aged dogs (4-10 years old).
Spotting the Signs of a Slow Metabolism
Because thyroid hormone affects the whole body, the signs can be vague and come on very gradually.
- •Weight Gain without an Increase in Appetite: This is a classic sign. Your dog is packing on the pounds, but you haven't been feeding them any more food.
- •Lethargy and Mental Dullness: They are lazy, sluggish, and just don't seem to have any energy. They may not be interested in playing and may sleep more than usual.
- •Heat-Seeking Behavior: Because their metabolism is slow, they have a hard time staying warm. You might find them seeking out sunny spots or lying near heat vents.
- •Skin and Coat Problems: This is a very common sign.
- •Symmetric Hair Loss (Alopecia): Often, the hair loss is on both sides of the body and spares the head and legs.
- •"Rat Tail": They can lose the hair on their tail, leaving it looking like a rat's tail.
- •Dull, Brittle Coat.
- •Recurrent Skin Infections.
- •Dark Pigmentation of the Skin.
- •Neurological Signs: In some cases, hypothyroidism can cause neurological problems like weakness, wobbliness, and facial nerve paralysis.
How Vets Diagnose Hypothyroidism
If your vet suspects hypothyroidism based on the clinical signs, they will recommend a blood test. However, diagnosing hypothyroidism is not always as simple as just measuring the thyroid level.
- •Screening Tests: A general blood panel might show a high cholesterol level, which is a clue for hypothyroidism. A screening T4 (the main thyroid hormone) level can be run, but many things can falsely lower a dog's T4 level (a condition called "euthyroid sick syndrome").
- •The Gold Standard Diagnostic Panel: To get a definitive diagnosis, your vet will send out a full thyroid panel to a diagnostic lab. This panel typically includes:
- •Total T4
- •Free T4 (fT4): This is a measure of the active form of the hormone and is less affected by other illnesses.
- •TSH (Thyroid Stimulating Hormone): TSH is produced by the pituitary gland in the brain to tell the thyroid to make more hormone. In a hypothyroid dog, the brain is screaming at the thyroid to work, so the TSH level is often high.
A dog with classic hypothyroidism will have a low T4 and Free T4, and a high TSH.
Treatment: A Simple Pill
The great news is that hypothyroidism is very easy and inexpensive to treat! The treatment is simply to replace the missing hormone.
- •Levothyroxine: This is a synthetic thyroid hormone that is given as a pill, usually twice a day, for the rest of the dog's life.
That's it! The medication is very safe. Your vet will recheck the thyroid levels a few weeks after starting the medication to make sure the dose is correct, and then will typically monitor the levels once or twice a year.
Prognosis
The prognosis for dogs with hypothyroidism is excellent! Once they are on the medication, you will see a dramatic improvement.
- •Within a week or two, their energy level and mental alertness will improve.
- •The weight will start to come off over the next few months.
- •The skin and coat problems will take the longest to resolve. It can take 4-6 months for the hair to start growing back.
With simple, lifelong supplementation, a hypothyroid dog can live a completely normal, happy, and healthy life.
Sources & Further Reading:
- •VCA Animal Hospitals - Hypothyroidism in Dogs
- 1Merck Veterinary Manual - Hypothyroidism in Animals