10 Signs of Hypothyroidism in dogs

Hypothyroidism is one of the most common endocrine disorders affecting dogs, particularly middle-aged and large-breed dogs. It occurs when the thyroid gland, located in the neck, fails to produce sufficient thyroid hormones. These hormones are crucial for regulating the body’s metabolism, and their deficiency can lead to a wide range of clinical signs affecting multiple systems in the body.

In our blog, we’ll cover the causes, symptoms, diagnosis, treatment, and management of hypothyroidism in dogs to help pet owners better understand this condition.

What is Hypothyroidism?

Hypothyroidism in dogs is primarily the result of decreased production of thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3), which play vital roles in regulating metabolism, body temperature, heart function, and other essential physiological processes.

Causes of Hypothyroidism in Dogs

Identifying the exact cause of hypothyroidism in dogs can be challenging, but around 90% of cases fall into one of these categories:

• Thyroiditis: This occurs when the immune system mistakenly attacks the thyroid gland, destroying healthy tissue. Known as autoimmune thyroiditis, it’s typically hereditary.

• Atrophy: In this case, normal thyroid tissue is gradually replaced by fat and connective tissue.

Other Contributing Factors

In recent years, fresh feeding for dogs has become increasingly popular. However, with this trend comes a lot of misinformation about canine nutrition, leading to many owners feeding their dogs unbalanced or deficient diets. Iodine, a vital trace mineral for healthy thyroid function and the production of T4 and T3 hormones, is often lacking in these meals. An iodine deficiency or excess can cause thyroid problems.

Kelp is a common source of iodine in home-prepared or commercial fresh foods, but it’s rarely included in online recipes, or it’s not used in the correct amounts. T4 contains four iodine molecules, and T3 contains three, so without sufficient iodine, the body can't produce enough thyroid hormones. It's important to note that hereditary thyroiditis is not caused by iodine deficiency, but over-supplementing with iodine can lead to an overproduction of T4 and T3, potentially triggering an immune response that damages the thyroid gland.

10 Symptoms of Hypothyroidism

Recognizing the signs of hypothyroidism in dogs is crucial when discussing the condition with your vet. Testing without clinical symptoms can be difficult, so knowing the indicators helps.

1. Weight Gain Despite Reduced Calories
   This is a well-known symptom, as hypothyroidism slows the metabolic rate, often leading to weight gain even when calorie intake is reduced. However, weight gain alone may not justify testing, so keeping a food diary or consulting with a canine nutritionist can help.

2. Hair Loss and Changes in Hair Texture
   Hair loss, typically on the flanks and base of the tail, can occur along with a coarse or bristle-like regrowth. The coat may also become dull or resemble a soft, puppy-like texture. However, hair loss may develop slowly over years, so don’t rely on this symptom alone.

3. Skin Changes
   Thickened skin, especially in areas of hair loss, may appear darker (hyperpigmentation). Folliculitis, characterized by raised bumps that scab over, can also develop, particularly on the back and base of the tail. Regular coat inspections are essential, especially in long-haired dogs.

4. Recurring Yeast and Ear Infections
   Yeast infections, particularly in the ears, can be a sign of hypothyroidism. A dog with a compromised immune system may struggle with leaky gut syndrome, creating an environment for yeast to thrive, despite ongoing treatment.

5. Fertility Issues and Irregular Heat Cycles
   Hypothyroidism can affect fertility in both male and female dogs. Females may experience irregular heat cycles, false pregnancies, or difficulty conceiving, while males may have low libido or sperm count.

6. Behavioral Changes
   Unusual behavior is often overlooked as a symptom. Dogs may exhibit excessive barking, aggression, anxiety, or depression. They may also appear hyperactive or unresponsive, with symptoms resembling separation anxiety.

7. Lethargy
   A common warning sign is reduced energy, especially during walks. Affected dogs may sleep excessively or require coaxing to eat.

8. Joint Pain or Swelling
   Some dogs may develop an unusual gait, as seen in cases where dogs “hop” on their front legs. Wobbly legs, joint pain, and swelling can also be symptoms.

9. Cold Intolerance
   Since the thyroid helps regulate body temperature, dogs with hypothyroidism may seek out warmth, often lying by fires or radiators. They may also be reluctant to go outside in cold weather.

10. Breathing Issues or Change in Bark
    Though rare, swelling in the neck that causes breathing difficulties or a change in bark can be an early symptom. These signs may be subtle but shouldn’t be ignored.

Consulting with Your Vet

Hypothyroidism is a manageable condition, and early detection allows for effective treatment. When visiting your vet, having a symptom diary can help convey both physical and behavioral changes. It’s important to push for comprehensive testing rather than treating individual symptoms. For instance, addressing recurring ear infections with steroids and antibiotics may not solve the underlying issue.

What Tests to Request

To properly diagnose hypothyroidism, request a full thyroid panel, including:

• T4 (Total T4): This alone is not sufficient to diagnose hypothyroidism, as it won’t detect autoantibodies.

• Free T4: A more accurate measurement, less affected by medications.

• TSH: As T4 levels drop, TSH typically increases.

• T3 and Free T3: These levels may be high in dogs with autoantibodies.

• TgAA: Elevated levels of this antibody indicate autoimmune thyroiditis.

Interpreting Test Results

Ensure that test results are correctly interpreted and request to review the levels yourself. Proper dosing of thyroid medication is critical, and should be adjusted based on your dog’s size, age, and breed. Puppies and senior dogs may metabolize the medication differently.

Administering Medication

Here are a few key tips for giving your dog thyroid medication:

• Administer the medication twice a day, 12 hours apart where possible, to maintain consistent hormone levels.

• Avoid giving the medication with a full meal, as calcium can hinder absorption.

• Give the medication one hour before or three hours after meals.

• Avoid soy-containing foods, as these can also affect absorption.

• Re-test thyroid levels 4–6 weeks after any dosage change or when starting treatment.

References

• W. Jean Dodds, DVM, Diana R. Laverdure. The Canine Thyroid Epidemic: Answers You Need for Your Dog.

• Cornell University College of Veterinary Medicine. Hypothyroidism in Dogs.

• GS Haritha, G Saritha, K Nalini K. Malasseziosis Associated with Hypothyroidism - A Clinical Report in a Dog. Dairy and Vet Sci J. 2017; 2(1): 555581. DOI: 10.19080/JDVS.2017.02.555581.