Is my dog hypothyroid?
Hypothyroidism is a common hormonal disorder in dogs. Continue reading to learn about the signs, causes, diagnosis, and treatment of canine hypothyroidism.
What is the thyroid?
The thyroid is a pair of glands that are located in the neck on each side of the trachea. There is a smaller gland on top of the thyroid gland called the parathyroid gland. These glands are small and rarely felt/palpated.
The thyroid gland produces various types of thyroid hormones, the most important being T3 and T4. The pituitary gland in the brain produces TSH (Thyroid Stimulating Hormone) to trigger the thyroid gland in the neck to release the thyroid hormones.
What is hypothyroidism?
Hypothyroidism is an endocrine disease that is most often caused by the destruction of thyroid gland tissue and replacement with scar tissue or other cell types that cannot produce the thyroid hormones. Rarely, a tumor on the thyroid or pituitary gland can cause hypothyroidism, but this accounts for less than 5% of cases. Hypothyroidism is most common in middle age or older adult dogs.
Clinical Symptoms of Hypothyroidism in Dogs
Clinical symptoms tend to develop when over 75% of the thyroid gland is no longer functioning. Changes to the skin and coat are the most common symptoms. If your dog has hypothyroidism, you might also notice:
- Weight gain without a big increase in appetite
- Poor hair coat: dry, brittle, and dull fur
- Hair loss, often on both sides of the body, on the lower chest and tail most commonly
- Increased occurrence of skin infections, often bacterial or yeast
- Thickened skin or blackness to skin (hyperpigmentation)
- Weakness or ataxia (abnormal gait)
- Low heart rate and possibly abnormal heartbeat
- Dry eye, eye ulcers, white plaques developing on the eye
- Facial nerve paralysis causing drooping of the lips or eyes
Diagnosing Hypothyroidism in Dogs
Blood work is needed to diagnose hypothyroidism. Your vet may recommend additional thyroid testing, even if your dog isn’t showing symptoms, if their routine lab work shows a low red blood cell count (anemia) and high cholesterol and lipid levels.
Many vets start routine screening of baseline thyroid levels around 7 years of age. If this value, the T4, comes back low, additional testing is indicated to verify hypothyroidism. The T4 level can be low if your dog is sick or stressed for any other reason, called Euthyroid Sick Syndrome, and may not be true hypothyroidism. The additional testing can help determine if your pup really is hypothyroid.
The ideal thyroid panel will test for T4, T3, Free T4 by ED, TSH, and Thyroid Autoantibodies. This type of comprehensive panel is often $200-300 or more, but it’s worth it to know if lifelong treatment for hypothyroidism is needed.
How Do I Treat My Dog’s Hypothyroidism?
Luckily, treatment is rather simple and inexpensive. Most dogs respond well to a daily or twice daily pill of Levothyroxine, a thyroid hormone supplement. Your vet will want to recheck the T4 level of your dog 3 to 4 weeks after starting treatment to ensure the dose is adequate and no adjustment is needed. Then, the thyroid level is typically monitored every 6 to 12 months once a good dose has been determined.
Clinical symptoms typically start to improve within 4 to 8 weeks after starting levothyroxine.
If your dog becomes agitated, loses weight, is drinking and urinating more, or doesn’t seem like themselves, be sure to let your vet know and get the T4 level checked as these can be signs the dose needs to be reduced.
If your dog has been diagnosed with a tumor on the thyroid gland or pituitary gland causing hypothyroidism, your vet can set up a referral to a local veterinary oncologist to discuss specific treatment options such as surgery, radiation therapy, and/or chemotherapy.
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