Hypothyroidism in Dogs

Dr. Jennifer Lavender

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What is the thyroid?
The thyroid is a gland found in the throat/neck of many species, including dogs.  Thyroid function is regulated by the pituitary gland in the brain.  The hormones produced by the thyroid ultimately set the “speed” for the body’s metabolism.  Because metabolic rate and function affects all cells – abnormalities in thyroid hormones cause clinical signs in multiple body systems.

Why does thyroid function decrease in dogs?

The primary causes for decreased thyroid function are:

  • Immune mediated destruction of the gland
  • Atrophy of the gland (may be sequela to above cause)
  • Dietary iodine deficiency
  • Congenital condition

What are the signs of decreased thyroid function?

  • Most common in middle-aged to older dogs
  • Predisposed breeds – Doberman, Golden retriever, Irish Setter, Great Dane, Dachshund, and Boxers. NOTE – the condition can be seen in ANY breed
  • Skin abnormality
    • Pigmentation
    • hair loss- often symmetrical and resulting in rat tail appearance
    • Itching, skin infections, dry coat
  • Obesity
  • Decreased energy level
  • Decreased heart rate
  • Eye clouding (corneal dystrophy) – most likely from increased triglycerdes
  • Possible connection – aggression, mega-esophagus, laryngeal paralysis, and infertility

How is hypothyroidism diagnosed?

Blood testing is used to diagnose hypothyroidism.  Many tests give information about the functionality of a dog’s thyroid gland.  These tests include – T4, T3, free T4, and TSH (thyroid stimulating hormone).  Your veterinarian may use a combination of these levels to determine your dog’s status.  Do not be surprised if initial levels warrant more specific thyroid tests to be added before starting medications.  Sometimes the diagnosis is confirmed by starting a trial of medication to see if clinical signs are improved.  Generally , levels are rechecked 1 month after starting medication.

What is the medication/treatment for hypothyroidism?

In short, treatment involves hormone replacement therapy with the T4 hormone.  Once initiated, treatment is usually life-long.