What is Hypothyroidism?
Canine hypothyroidism is a common endocrine disorder in dogs where the thyroid glands (located in the neck) produce insufficient amounts of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). These hormones play a critical role in regulating your dog’s metabolism, growth, and overall energy levels.
Common Breeds at Risk
While hypothyroidism can affect any dog, it is more common in the following breeds:
- English Setter
- Dalmatian
- Basenji
- Boxer
- Rhodesian Ridgeback
- Maltese
- Beagle
- Cocker Spaniel
- Shetland Sheepdog
- Siberian Husky
- Border Collie
- Akita
- Old English Sheepdog
- Golden Retriever
Causes of Hypothyroidism
The most common cause is autoimmune thyroiditis, where your dog’s immune system mistakenly attacks and destroys the thyroid glands. Other causes include thyroid gland atrophy, tumors, and rarely, congenital hypothyroidism.
Signs and Symptoms to Watch For
Since thyroid hormones influence metabolism, a lack of them can lead to various signs:
- Weight gain despite normal or decreased appetite
- Lethargy or decreased activity levels
- Cold intolerance (seeking warmth or shivering)
- Hair loss or thinning coat, often in symmetrical patterns
- Dry, flaky skin
- Slow heart rate
- Muscle weakness or atrophy
- Excessive shedding or changes in coat texture
- Recurrent infections, particularly skin or ear infections
- “Tragic” facial expression due to muscle weakness and skin changes
Diagnosis
Hypothyroidism is diagnosed through a combination of clinical signs and laboratory tests, which may include:
- Thyroid hormone tests: T4, free T4, T3, and Thyroid Stimulating Hormone (TSH)
- T3 and T4 autoantibody tests: helps identify autoimmune thyroiditis
- Complete blood count and chemistry panel: checks for changes related to low thyroid levels
Treatment
Thyroid Hormone Replacement
With an accurate diagnosis, appropriate treatment, and monitoring, hypothyroidism carries a good prognosis. Treatment involves synthetic thyroid hormone replacement, usually in the form of levothyroxine (Thyro-Tabs). Levothyroxine is typically given orally once or twice daily, and the correct dosage varies based on the dog’s weight and response to treatment. The dose will be adjusted to achieve optimal hormone levels and improve clinical signs.
Monitoring Response
The most important indicator of successful treatment is clinical improvement. Improvements in lethargy and mental alertness occur within 2 weeks, while dermatological issues and body weight may take several months to improve.
Potential Side Effects
Although levothyroxine is generally well-tolerated, some dogs may develop signs of over-treatment (excessive thyroid hormone):
- Increased heart rate
- Restlessness or hyperactivity
- Increased thirst and urination
- Vomiting or diarrhea
If any of these signs occur, your veterinarian may need to adjust the dosage.
Follow-Up Care and Monitoring
Dogs with hypothyroidism require regular monitoring to ensure optimal treatment:
- Initial blood test: 4 weeks after starting medication. Important: The test must be performed 4-6 hours after the morning pill
- Follow-up thyroid level checks: 3 months and 6 months after the first recheck
- Long-term: Complete blood count, chemistry panel, and thyroid levels tested once to twice yearly
Weight Management
Hypothyroid dogs are prone to weight gain, even with treatment. It’s essential to monitor your dog’s weight and adjust their diet and exercise routine accordingly. Your veterinarian can help create a proper diet plan if weight becomes an issue.
Prognosis
With appropriate treatment and routine follow-up care, most dogs with hypothyroidism can live long and healthy lives. Symptoms such as weight gain, lethargy, and coat changes typically improve after starting treatment. However, lifelong treatment with thyroid medication is required, and occasional adjustments in dosage may be needed over time. If left untreated, this condition can lead to more severe complications.
Regular communication with your veterinarian about your dog’s progress and any concerns is essential for the successful management of hypothyroidism.
