Hypothyroidism In Dogs

Dr. Teresa Garden

By Teresa Garden, DVM

Hypothyroidism is the most commonly diagnosed endocrinopathy in the dog. It is also OVER diagnosed and this can lead to unnecessary treatment. Hypothyroidism results in a decreased production of thyroid hormone from the thyroid gland. Ninetyfive percent of the time the disease is caused by destruction of the thyroid gland from lymphocytic thyroiditis, thyroid atrophy, or a tumor. Lymphocytic thyroiditis, caused by an immune-mediated mechanism, is the most common cause of hypothyroidism in our dogs. Clinical signs occur when 75% of the gland is destroyed.

Any breed of dog may develop hypothyroidism but some breeds are genetically predisposed. Thyroiditis is heritable in the Beagle, Borzoi, Golden Retriever, Great Dane, Irish Setter, Doberman Pinscher, and Old English Sheepdog. The disease occurs in young to middle age dogs. Spayed females and neutered males are at increased risk compared to sexually-intact dogs.

Clinical signs of hypothyroidism are subtle and have a gradual onset. Symptoms to watch for are lethargy, exercise intolerance, heat-seeking, weight gain, mental dullness, decreased appetite, and constipation. Symmetrical thinning hair or hair loss on the back and sides that does not itch may be a common symptom noticed by pet owners. This may be accompanied by a “rat tail”…hair loss on the tail. Other dermatological symptoms are hyperpigmentation, failure of hair growth, pyoderma, and seborrhea.

Blood tests are run to properly diagnose hypothyroidism and to rule out other diseases that may present with similar symptoms. Hypothyroid dogs will have an increase in their cholesterol, triglycerides, and liver enzymes. T4, the major thyroid hormone secreted into the blood stream, is a screening test and will be low in a hypothyroid dog. T4 is often included in routine blood profiles run by veterinarians. T4 is a sensitive but not specific test for canine hypothyroidism. The vast majority of hypothyroid dogs will have low T4 but some normal dogs with other medical problems may have a low T4. Systemic diseases such as diabetes, Cushing’s, renal failure, Addison’s disease, hepatic failure, and infection, can lower T4 levels. Certain breeds such as Greyhounds, Whippets, Salukis, and Scottish Deerhounds will have T4 levels lower than other breeds. There are drugs which can also alter thyroid levels. These include phenobarbital, prednisone, sulfonamides, clomipramine, and some NSAIDS.

Once it is suspected a dog may be hypothyroid, additional thyroid hormones need to be measured to confirm or rule out hypothyroidism as a diagnosis. Free T4 is more specific for hypothyroidism because it is less affected by non thyroid illnesses and drugs. It will be low in 98% of cases of hypothyroidism. TSH (Thyroid Stimulating Hormone) will be measured as well. It will be elevated 60-75 % of the time. Free T3, Anti-Thyroglobulin Antibody, and Anti T3 and T4 Antibodies are also included and measured in diagnostic thyroid profiles.

Once a diagnosis has been established treatment can begin. Synthetic thyroid hormone replacement products are the mainstays of treatment. Synthetic hormone is preferable over those of animal origin because they are more stable and better standardized for potency. Brand name products (Soloxine or Thyro-Tabs) are preferred over generic products. Some generics may have less hormone than is printed on the label or may vary pill to pill. Dosing is either once or twice daily depending on the individual patient’s response to treatment. Clinical improvement should be observed in 4-6 weeks from initiation of therapy. Skin and hair abnormalities may take 2-3 months to resolve. T4 levels are measured about a month after starting therapy and should be normal.

Holistic modalities can help hypothyroidism and tend to focus on the autoimmune process of the disease. Therapeutic nutrients, medicinal herbs, and biological therapies can help quiet the autoimmune process and slow organ degeneration. Nutrients nourish organ cells and help control ongoing inflammation. Canine Thyroid Support, Thyrotrophin PMG, and Pituitrophin PMG are nutritional supplements from Standard Process used to decrease cellular inflammation and improve organ function. They will help to spare thyroid and pituitary glands from further immune attack, cascading inflammation, and eventual degeneration. Antioxidants can be employed to slow progression of immune-mediated hypothyroidism. Alpha-lipoic acid is a potent antioxidant proved to reduce stress and inflammation. It has been shown to increase the effectiveness of other antioxidants such as Vitamin C, Vitamin E, Coenzyme Q10, and glutathione. Coenzyme Q10 is a strong antioxidant that helps reduce the associated inflammation that is the predecessor to many chronic diseases. Chinese herbal formulas have also been used successfully to treat hypothyroidism in dogs in lieu of thyroid replacement hormone. The formula must be matched to the symptoms of the patient and prescribed by an experienced veterinarian certified in TCM. It may be a good idea to consider discontinuing vaccination in cases of hypothyroidism. Links are increasingly being made between the use of polyvalent vaccines and autoimmune inflammation of the thyroid gland.

Hypothyroidism has a good prognosis once properly diagnosed and treated. It is incumbent upon the veterinarian to consider history, physical exam findings, and complete and thorough thyroid blood test results to establish or rule out this disease. It is our goal as veterinarians to properly diagnose instead of over-diagnose hypothyroidism.

Dr. Teresa Garden is chief veterinarian/owner of Animal Health & Healing, a full-service holistic and conventional veterinary practice in the Maplewood/Richmond Heights area. 314-781-1738.