Hypothyroidism is one of the most common medical disorders of dogs. Classic symptoms include weight gain without an increase in appetite, sluggishness, a dull hair coat with flaky skin that is not red or itchy, cold intolerance, and hair loss on the trunk, back of the rear legs, and the tail. Other abnormalities may include thickening of the facial skin, muscle loss, nerve problems, non-painful lameness, megaesophagus and in some cases seizures.
A veterinarian will typically perform a physical exam and submit a blood panel, including a common screening test, TT4 (Total Thyroxin). However, a low TT4 alone is NOT an accurate indicator of hypothyroidism in dogs. A definitive diagnosis needs to be made by testing the "free T4" by Equilibrium Dialysis and/or potentially a complete thyroid hormone panel. A low level of "free T4 (ED)" along with clinical signs confirms hypothyroidism and thyroid replacement hormone can start.
What Does The Thyroid Gland Do?
The thyroid is located in the neck near the trachea. It produces thyroxine which controls your dog’s metabolism. The thyroid gland is regulated by the pituitary gland, which is located at the base of the brain. When your dog’s thyroid is not producing enough thyroxine to engage in regular activity, it is called hypothyroidism. This type of thyroid condition is the most common among dogs.
What Causes Hypothyroidism?
The most common causes of hypothyroidism are typically caused by one of two diseases: lymphocytic (autoimmune) thyroiditis or idiopathic thyroid gland atrophy. These account for more than 95% of cases in dogs. In lymphocytic thyroiditis, your dog’s immune system intrudes upon the thyroid as it thinks it is a foreign threat. The body then produces antibodies to destroy the functional thyroid tissue. In idiopathic thyroid gland atrophy, the thyroid gland is replaced by fatty tissue. It is unclear why these conditions occur. The other 5% of cases are due to rare disorders, including thyroid cancer.
Here are Top 10 Facts About Hypothyroidism
- Hypothyroidism usually occurs in dogs between the ages of four and six years old.
- Any dog, including mixed breeds, can develop hypothyroidism. However, it is most often found in medium-to-large-size breeds —Doberman Pinschers, Golden Retrievers, Irish Setters, Great Danes, and Boxers—as well as some smaller breeds, including Cocker Spaniels, Dachshunds, and Miniature Schnauzers. These breeds likely inherit a genetic disposition for hypothyroidism.
- To date, there is no evidence that vaccines induce the disorder.
- Classical symptoms of hypothyroidism only appear once >70% of the thyroid gland is damaged. Once the thyroid is damaged, it doesn't regenerate. Annual exams and bloodwork may allow for early recognition of thyroid disease.
- Nearly 33% of hypothyroid dogs tend to have raised fasting cholesterol and triglycerides, raised liver values, and mild anemia along with a low TT4 and free T4.
- Dogs who have higher TSH levels suggest to vets that hypothyroidism is a possible diagnosis as high TSH counts are found in 70% of hypothyroidism diagnoses.
- Once a definitive diagnosis of hypothyroidism is made, management and treatment are affordable. Dogs typically respond well to a long-term, twice a day dosage protocol of oral levothyroxine. Most dogs will show improvement - increased energy, shinier hair coat, hair regrowth, and weight loss - within three to four weeks of beginning hormone replacement therapy.
- There are situations when a dog's thyroid level is considered "atypical" - meaning their bloodwork doesn't correspond with their clinical signs. This is classified as, euthyroid sick syndrome. It occurs when a dog may is suffering from a "nonthyroidal" illness that lowers T4 despite normal thyroid function -
- Certain medications can cause decreased thyroid levels including phenobarbital (anticonvulsant), trimethoprim-sulfonamide (antibiotic), zonisamide (anticonvulsant), clomipramine (antidepressant), and steroid medications (drugs that stop inflammation, such as oral or topicals for ears, eyes, and skin). So, if your dog is being given one of these medications, one way to clarify blood results is to work with your vet to safely wean him off the medication. After halting the medication for the prescribed period, blood work can be rechecked. If it’s not possible to stop a medication, a six-to-eight-week levothyroxine trial is sometimes employed.
- Adding to the confusion, certain breed types - athletic dogs, Sight Hounds, Basenjis - typically have thyroid levels that are normally low. It is critical to work with a veterinarian that understands how to interpret these tests.
- Experts correlate hypothyroidism to an immune-mediated disorder. There are supplements you can add to support your dog's immune system.
- Omega 3 fatty acids: these fats aid in combating dry, flaky skin and supporting neurological and cognitive function.
- Probiotics: supplementing the gut with good bacteria may help reduce inflammation in the gut and support the immune system.
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Paying attention to changes in your dog’s routine can greatly improve treatment options as the earlier the detection, the higher the chance of a full recovery.
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