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Hypothyroidism in Dogs

hypothyroidism in dogs


A common disease in dogs, hypothyroidism is an endocrine disease that occurs when the thyroid gland does not produce or release adequate amounts of the hormones known as T3, or triiodothyronine, and T4, or thyroxine. An essential gland, the thyroid produces several types of hormones, including T3 and T4, both of which are required for normal metabolism. Metabolism refers to the chemical processes necessary for life that convert food into energy. Hypothyroidism in dogs affects a range of life-sustaining activities within the body, slowing down metabolic processes.

What Causes Canine Hypothyroidism?

Causes for hypothyroidism in dogs include:

  • Unknown etiology, which means the origin is not known
  • Congenital disease
  • Iodine deficiency
  • Cancer
  • Result of surgery or medical treatment

The most common diagnosis underlying hypothyroidism in dogs is lymphocytic thyroiditis, an immune-mediated disease some breeds are predisposed to inherit. The lymphocytic thyroiditis causes the destruction of the thyroid gland over time; only when the gland is about 70 percent gone do clinical signs begin to show. The second most common diagnosis is idiopathic thyroid gland atrophy, a degenerative disease of unknown origin that develops spontaneously. More than 95 percent of clinical cases of hypothyroidism in dogs result from the destruction of the thyroid gland by one of these two diagnoses.

Only five percent of hypothyroidism cases in dogs are from other causes, including cancer and iodine deficiency.

Breeds More Likely to Have Hypothyroidism

Though hypothyroidism affects all breeds of dogs, the condition is found more frequently in certain breeds. Hypothyroidism in dogs usually happens in middle-aged dogs aged four to 10 years of medium to large breeds, particularly:

Signs and Symptoms of Hypothyroidism in Dogs

Clinical signs of low thyroid function in dogs can be nonspecific, which sometimes results in overdiagnosis of hypothyroidism. The most common signs of hypothyroidism in dogs include:

  • Lethargy and reduced activity
  • Unexplained weight gain
  • Generalized weakness
  • Reduced tolerance to cold temperatures
  • Excessive shedding of hair
  • Excessive scaling of skin
  • Alopecia, or hair loss, over the body
  • Dull hair coat
  • Poor hair growth
  • Ear infections, with ear pain, redness, and odor
  • Mental dullness
  • Recurring, itchy skin infections

Less common signs a dog has hypothyroidism include tilting the head to one side, seizures, and infertility. Some hypothyroid dogs experience an accumulation of substances called mucopolysaccharides, which can cause the face muscles to droop and give the dog a “tragic” facial expression.

Diagnosis and Treatment Options for Dogs With Hypothyroidism

Making a diagnosis of hypothyroidism in a dog requires multiple hormone tests. Veterinarians should test a dog for hypothyroidism only if the disease is strongly suspected based on the dog’s history and findings from physical examination. Elevated cholesterol levels support suspicions of hypothyroidism, since about three-fourths of hypothyroid dogs have high cholesterol.

If tests confirm the dog is hypothyroid, the vet will prescribe synthetic hormones. Research shows that most dogs can be regulated with a once-daily pill of the drug levothyroxine. A modification of the dog’s diet, including less fat, usually is recommended during therapy’s initial phase. Successful treatment requires conscientious compliance with giving the prescribed drugs and following the recommended diet.

Most dogs respond well to treatment and experience increased activity levels and mental alertness after only a short time. However, lifelong therapy is required to regulate the condition. Periodically, the veterinarian might adjust the dosage of the synthetic hormones.

Cost: $100 to $200 for the tests. Ongoing medications typically cost $10-30 per month.

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