31 Mar Hypothyroidism in Dogs: Understanding, Managing, and Living with the Condition

Hypothyroidism in dogs is a medical condition characterised by an underactive thyroid gland in the neck. The thyroid gland produces thyroid hormones, vital in regulating the body’s metabolism, energy levels, and other essential functions.

Hypothyroidism occurs when a dog’s thyroid gland fails to produce sufficient thyroid hormone. This deficiency can occur for various reasons, including autoimmune diseases, thyroid gland abnormalities, or congenital issues.

Thyroid hormones are crucial in regulating the body’s metabolism of fats, proteins, and carbohydrates. In dogs, a deficiency of these hormones can cause a slowdown in the metabolic rate, resulting in various symptoms.

Causes of Hypothyroidism in Dogs

1. Autoimmune Thyroiditis: In autoimmune thyroiditis, the dog’s immune system mistakenly attacks its thyroid gland, leading to inflammation and damage. This immune-mediated destruction of thyroid tissue disrupts the gland’s ability to produce adequate thyroid hormone.
2. Congenital Hypothyroidism: Some dogs may be born with a genetic predisposition to hypothyroidism, resulting from abnormal development or function of the thyroid gland from birth. Congenital hypothyroidism is relatively rare but can occur in certain dog breeds.
3. Thyroid Gland Atrophy: As dogs age, their thyroid glands may undergo atrophy or shrinkage, reducing their ability to produce thyroid hormones. This age-related decline in thyroid function can contribute to the development of hypothyroidism in senior dogs.
4. Iodine Deficiency: Iodine is essential for synthesising thyroid hormones. In areas where dietary iodine levels are insufficient, dogs may develop hypothyroidism due to a lack of iodine necessary for thyroid hormone production.
5. Thyroid Tumours or Neoplasms: Tumours or neoplastic growths within the thyroid gland can disrupt its normal function, leading to decreased hormone production. Benign and malignant tumours can interfere with thyroid hormone synthesis and secretion, resulting in hypothyroidism.
6. Medications or Treatments: Some drugs or treatments, like radioactive iodine therapy or surgical removal of the thyroid gland (thyroidectomy), can inadvertently damage or impair thyroid function, resulting in hypothyroidism as a side effect.
7. Environmental Factors: Some environmental conditions, such as exposure to toxins, pollutants, or endocrine-disrupting chemicals, can interfere with thyroid function and contribute to developing hypothyroidism in susceptible dogs.
8. Other Medical Conditions: Underlying medical conditions, such as chronic renal failure, pituitary gland disorders, or certain medications used to manage other health issues, can indirectly affect thyroid function and contribute to hypothyroidism.

Symptoms of Hypothyroidism in Dogs

Common symptoms of hypothyroidism in dogs include:

1. Lethargy: Dogs with hypothyroidism often lack energy and motivation. They may seem unusually tired or reluctant to engage in physical activities.
2. Weight Gain: Hypothyroidism can cause dogs to gain weight despite maintaining a normal diet and exercise routine. This weight gain is often gradual and may be accompanied by a decrease in muscle mass.
3. Hair Loss: One of the hallmark signs of hypothyroidism is bilateral symmetrical hair loss, particularly on the trunk, tail, and hindquarters. The coat may appear thin, dull, and dry, with patchy areas of baldness.
4. Dry, Flaky Skin: Dogs with hypothyroidism may develop dry, flaky skin, which can become itchy and irritated. Also, they may scratch or lick excessively, leading to further skin damage and potential secondary infections.
5. Cold Intolerance: Hypothyroid dogs may exhibit intolerance to cold temperatures, seeking out warm spots to lie down or curling up in blankets to stay warm. They may shiver or tremble, even in mild or moderate weather conditions.
6. Sluggishness: Dogs with hypothyroidism may appear mentally dull or slow to respond to stimuli. They may also lack enthusiasm for activities they once enjoyed and be less responsive to commands or training cues.
7. Muscle Weakness: Hypothyroidism can lead to muscle weakness and stiffness, particularly in the hind limbs. Dogs may have difficulty climbing stairs, jumping, or performing other physical tasks.
8. Changes in Behaviour: Some dogs with hypothyroidism may exhibit changes in behaviour, such as increased irritability, aggression, or anxiety. They may also become more withdrawn or less interactive with their owners and other pets.
9. Ear Infections: Chronic ear infections may occur due to hypothyroidism, often due to changes in skin texture and increased susceptibility to yeast or bacterial overgrowth in the ear canal.

Diagnosis of Hypothyroidism in Dogs

1. Clinical Evaluation: The veterinarian will begin by conducting a comprehensive physical examination of the dog, noting any symptoms suggestive of hypothyroidism, such as lethargy, weight gain, hair loss, and skin abnormalities. The owner’s detailed medical history is also valuable in assessing the dog’s overall health and any relevant past medical conditions.
2. Thyroid Function Tests: Blood tests are essential for evaluating thyroid hormone levels in dogs suspected of having hypothyroidism. The most commonly used thyroid function tests include:

• • Total Thyroxine (T4) Level measures the total concentration of circulating thyroxine in the bloodstream. Low T4 levels are indicative of hypothyroidism.
  • Free Thyroxine (fT4) Level: This assesses the biologically active form of thyroxine that is unbound and available for cellular uptake. Low levels of fT4 support the diagnosis of hypothyroidism.
  • Thyroid Stimulating Hormone (TSH) Level: Measuring TSH concentration can help differentiate primary from secondary hypothyroidism. Elevated TSH levels in conjunction with low T4 levels indicate primary hypothyroidism, whereas low or normal TSH levels suggest secondary hypothyroidism.

3. Additional Tests: Additional tests may be needed to rule out other causes or assess the extent of thyroid dysfunction in dogs. These tests may include:

• • Thyroid Antibody Testing: Assessment of thyroid autoantibodies can help diagnose autoimmune thyroiditis, a common cause of hypothyroidism in dogs.
  • Thyroid Ultrasound: Imaging studies such as ultrasound may be performed to evaluate the thyroid gland’s size, shape, and texture and detect any structural abnormalities or neoplastic growths.

Treatment Options for Hypothyroidism

1. Thyroid Hormone Replacement Therapy: Treating hypothyroidism involves oral administration of synthetic thyroid hormone supplements, such as levothyroxine sodium (L-thyroxine). These medications provide the dog’s body with the necessary thyroid hormones, which are deficient due to the underactive thyroid gland. 
2. Individualised Dosage Adjustment: Determining the appropriate dosage of thyroid hormone replacement medication is crucial for achieving optimal therapeutic effects while minimising potential side effects. The veterinarian may initially prescribe a starting dose based on the dog’s weight and severity of hypothyroidism. 
3. Consistent Administration: Dog owners must administer thyroid hormone replacement medication consistently and as directed by the veterinarian. Missing doses or inconsistent administration can lead to fluctuations in thyroid hormone levels, compromising the effectiveness of treatment and exacerbating symptoms of hypothyroidism.
4. Monitoring Thyroid Function: Regular blood tests are necessary to monitor thyroid hormone levels, assess response to treatment, and ensure levels remain in the target range for dogs. Veterinarians may recommend periodic blood tests, typically every 6 to 12 months, to evaluate thyroid function and adjust medication dosage as necessary.
5. Dietary Considerations: While nutritional modifications are not typically the primary treatment for hypothyroidism in dogs, maintaining a balanced diet is essential. Some veterinarians may recommend specific dietary supplements or formulations to support thyroid function or address concurrent nutritional deficiencies.
6. Lifestyle Management: Supporting the dog’s overall health with regular exercise, weight management, and appropriate environmental conditions can complement medical treatment for hypothyroidism. Providing a supportive and stress-free environment can help reduce the risk of exacerbating symptoms or complications associated with hypothyroidism.

Prevention Measures

1. Nutrition: Ensure your dog’s diet includes adequate levels of iodine, selenium, zinc, and omega-3 fatty acids, which are important for thyroid function. Choose high-quality commercial dog foods or consult a veterinary nutritionist to formulate a balanced homemade diet.
2. Regular Veterinary Check-ups: Schedule routine veterinary examinations for your dog at least once a year or as your veterinarian recommends. 
3. Environmental Factors: Minimise your dog’s exposure to environmental toxins and pollutants that may disrupt thyroid function. So, avoid exposing your dog to cigarette smoke, pesticides, herbicides, and other harmful substances. 
4. Maintain a Healthy Weight: regular exercise and a balanced diet can help to keep a healthy weight. Avoid overfeeding and monitor your dog’s calorie intake to prevent excessive weight gain.
5. Stress Management: Chronic stress can affect thyroid function in dogs. Minimise stressors in your dog’s environment Regular exercise, social interaction, and positive reinforcement training can help reduce stress levels in dogs.
6. Genetic Screening: If you’re considering breeding your dog, choose breeding stock that has been screened for hereditary conditions, including autoimmune thyroiditis. 

The Last Word

Hypothyroidism is a manageable condition in dogs with proper diagnosis, treatment, and ongoing care. By understanding the symptoms, seeking timely veterinary intervention, and providing consistent support, dog owners can help their furry companions live full and active lives despite the challenges posed by this condition.