Hypothyroidism in Dogs

The thyroid gland, located on either side of the wind pipe, secretes two hormones, thyroxin (T4) and triiodothyronine (T3) that are essential for the regulation of all the metabolic functions in the body. Dysfunction of the thyroid gland, or in the chemical pathways that utilize T4 and T3, can result in a number of clinical signs that may indicate a disrupted metabolism. Clinical signs of hypothyroidism in the dog cover a wide spectrum and reflect a decrease in thyroid function. They include:

  • Alterations in cellular metabolism which can result in weakness/stiffness, paralysis of the larynx or facial muscles, knuckling or dragging the feet, muscle wasting, megaesophagus, head tilt, and drooping eyelids.

  • Neuromuscular problems which can cause seizures, mental weakness, exercise intolerance, lethargy, weight gain, cold intolerance, mood swings, hyperexcitability, stunted grown, and chronic infections due to an impaired immune system

  • Dermatologic diseases that can be seen include dry, scaly skin (dandruff), dull or coarse hair coat, symmetrical hair loss, darkening of the skin, greasy skin, frequent bacterial and yeast skin infections, bad odor, and chronic ear infections.

  • Reproductive Disorders associated with low thyroid function include infertility, lack of libido, testicular atrophy, decreased sperm production and motility, absence of heat cycles, fake pregnancy, and weak/dying/still born pups.

  • Cardiac abnormalities seen with hypothyroidism include a slow heart rate (bradycardia), abnormal heartbeats, and physical heart problems (cardiomyopathies).

  • Gastrointestinal disorders seen include constipation, vomiting, or diarrhea.

  • Hematological disorders seen with low thyroid my include uncontrolled or abnormal bleeding, failure of the bone marrow to produce cells, anemia, low white blood cells, and low platelet numbers.

  • Ocular diseases connected to hypothyroidism can include lipid deposits in the corneal, corneal ulceration, uveitis, dry eye syndrome, and infection of the eyelid glands

  • Numerous other disorders have been connected to underactive thyroids and include a number of adrenal, pancreatic, and liver problems, sugar in the urine, and loss of smell and taste.

Left untreated, any number of the above disorders or symptoms can dramatically shorten a dog’s life and certainly decreases the quality of life.

Genetics can cause a predisposition for hypothyroidism but there are many environmental factors, such as diet/nutrition and exposure to toxins or chemicals that can trigger clinical disease. Many cases of hypothyroidism can be a result of the immune system ‘turning’ on its own thyroid and attacking the thyroid tissue.

Diagnosing hypothyroidism can be complex and includes a good physical exam, presence of clinical signs or symptoms, and special blood tests that measure the amount of T3 and T4 (and other related hormones) in the bloodstream. Antibodies against the thyroid can be measured if an autoimmune cause is suspected.

Treatment of hypothyroidism is relatively easy and most patients only need to take a small tablet, replacement thyroid hormone, twice daily. Lifelong supplementation is usually required and blood tests to monitor thyroid levels are recommended at specific intervals throughout treatment. In many cases, clinical signs and symptoms begin to resolve within the first month of treatment but chronic cases may take longer to show improvement.

If you think your dog may be suffering from hypothyroidism, please give us a call. We would happy to schedule an exam so our doctors can help determine if testing is warranted. 

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