You might first notice that your dog is gaining weight, although his appetite has not increased. Then he might get quiet – he doesn't want to play, he seems to sleep a lot and he gets really tired when you take him for a walk. You might see some skin changes or some hair loss. Your first tendency might be to blame it on the aging process. But don't do that yet. See your veterinarian first. Your dog-tired pet may be suffering from hypothyroidism.
Hypothyroidism is a disorder of the thyroid gland – two butterfly-shaped lobes located in the neck just below the voicebox. This gland is responsible for producing and secreting thyroid hormone (thyroxine), which affects nearly all body systems, but the most significant is the regulation of your dog's metabolic rate. In hypothyroidism, not enough thyroxine is produced, which causes slow metabolism.
Hypothyroidism is the most common endocrine disorder in dogs and most commonly develops between the ages of 4 to 10 years. It usually affects males and females equally and is more common in mid to large size breeds, such as Golden retrievers
Hypothyroidism can be divided into primary and secondary causes. Most cases are primary, which means that destruction of the thyroid gland itself is at fault. Most of these are thought to be caused by the dog's own immune system.
Lymphocytic thyroiditis – a genetically based disease that slowly destroys the dog's thyroid gland
Idiopathic follicular atrophy – a degeneration of the thyroid gland with no known cause
Thyroid neoplasia (cancer) or infection
Dietary iodine deficiency
Congenital causes (cretinism/dwarfism)
Surgical thyroidectomy (thyroid removal)
These causes relate to abnormalities of the pituitary gland, the gland in the brain that stores and secretes certain hormones. Secondary causes are any conditions that impair secretion of the thyroid-stimulating hormone by the pituitary gland for any reason.
What To Watch For
A deficiency of thyroid hormone affects the metabolic function of all organ systems. As a result, the symptoms are usually variable and non-specific. Although there is no one symptom that is diagnostic, several combined symptoms might make your veterinarian more suspicious. Symptoms may include:
Lethargy – lack of interest in play; frequent sleeping
Exercise intolerance – tiring out on walks
Weight gain – without an apparent gain in appetite
Cold intolerance – seeks out warm places to lie down
Slow heart rate – Bradycardia
Chronic skin disorders -- dry skin, hair loss
Hypothyroidism is not always a simple, straightforward diagnosis. Tests chosen will depend on the symptoms and the availability of different tests to your veterinarian. Proper diagnosis includes a combination of history, clinical signs, physical examination findings and diagnostic tests, including:
Complete blood count (CBC)
Thyroxine (T4) level
Thyrotropin (TSH) stimulation test
Thoracic (chest) and abdominal radiographs (X-rays) in certain cases
Fortunately, hypothyroidism is easily treated and includes putting your dog on a daily dose of synthetic thyroxine. Once treatment is started, it will continue for the rest of your dog's life.
At home you should administer all prescribed medication(s)and observe your dog closely for recurrence of symptoms or occurrence of other / opposite symptoms, such as hyperactivity or weight loss to assure the proper thyroid status is maintained and you are giving the proper dose of supplement. Also, see your veterinarian for periodic blood levels to monitor the thyroid level to ensure adequate drug dosage.
Hypothyroidism is an endocrine disorder and cannot be prevented. However, once treatment begins, the majority of the symptoms resolve. Lifelong administration of proper replacement therapy and periodic thyroid tests can help your dog maintain his health.
To learn more about hypothyroidism, please click on Hypothyroidism in Dogs.