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Canine hypothyroidism is a disease which is diagnosed quite often in Shibas. The thyroid gland, located on the trachea at the base of the neck, is best known for regulating the speed of metabolism of almost all body cells. Its function is to secrete the hormones called thyroxin (T4) and triiodithyronine (T3), throughout the dog's body. If the thyroid gland is unable to do its job properly, many different body systems can be affected, resulting in varied and sometimes contradictory clinical signs. A dog may only have a couple of symptoms or many. The most common clinical signs seen are:

• Behavioral Changes: Aggression, Fearfulness, Depression, Mood Swings, Anxiety, Phobias and Hyperactivity (less common). In most cases, behavioral signs are usually present before skin and coat changes.
• Weight gain: this can occur without an increase in appetite.
• Lethargic behavior: Lack of interest in playing, increase in sleep habits.
• Intolerance to exercise: Tiring easily on walks.
• Intolerance to cold: The dog is always cold and seeks out warm places such as heat vents or sunny spots.
• Hair loss/coat changes: Hair loss (alopecia) can be all over or in bilateral symmetrical patches on trunk. "Rat's tail" hair loss is common. Coat is usually dry, dull and hair is brittle, breaking off easily when touched. Hair grows back slower and frequent shedding is seen.
• Skin changes: Bacterial infections of the skin are common especially staphylococcus (staph) infections. Skin pigmentation may lighten, darken or thicken where hair loss has occurred. Skin is usually dry and scaly but can also sometimes be oily or greasy.
• Tragic expression: This is caused by thickening of the facial skin.
• Bradycardia: Slow heart rate
• Cardiac Arrhythmias: Irregular heartbeat
• Chronic or recurrent ear infections
• Seizures
• Infertility
• Diarrhea / vomiting
• Muscle pain, stiffness, weakness or loss

There are many causes of hypothyroidism.

• Idiopathic - of unknown origin
• Secondary - as a result of medications and diseases such as cancer or a pituitary disorder
• Autoimmune Thyroiditis - accounts for majority of cases/diagnosed most often

Autoimmune thyroiditis causes the dog's own immune system to attack the thyroid gland. In the beginning the dog will attempt to compensate by releasing more thyroxin, but eventually the gland is unable to secrete enough thyroid hormone, reserves are depleted, and the dog begins showing clinical signs of hypothyroidism.

Some breeds seem to have a higher incidence of this disease occurring than other breeds. Since there is a genetic component to thyroid disorders, dogs with this disease should never be used for breeding.

Hypothyroidism can often mimic other diseases so diagnosis should start with a visit to your vet. A complete examination will be done and questions will be asked about your dog's history, health and behavior. If your vet feels that hypothyroidism is possible then a blood sample will be drawn and tested. The tests used to measure thyroid hormone concentrations in the blood are:

Total T-4 (TT4): This is the test most commonly used. It measures the amount of total thyroxine in the blood. (Thyroxine is the main hormone secreted by the thyroid gland.) Certain drugs and medical conditions can lower T4 besides thyroid gland failure so please inform your vet of all medications your dog is taking.

Baseline T-3 : This test is not reliable when used alone. Hypothyroid dogs will often have normal concentrations of T3 in their blood. Occasionally hypothyroid dogs can form antibodies to T3 in the blood.

Free T-4: Free T4 concentration in the blood is a more accurate indicator of true thyroid gland functioning as it is less likely to be affected by medical conditions and medications. Measuring T4 by using equilibrium dialysis achieves more accurate results.

Baseline TSH test: This test is used to measure the level of Thyroid Stimulating Hormone. If used as part of a complete thyroid panel or with T4 it is a more accurate indicator of thyroid function.

TSH Response test : This test measures T4 concentrations in the blood before (baseline sample) and 6 hours after an injection of Thyroid Stimulating Hormone (TSH). If the level of TSH in the 6 hour blood test does not show a significant increase from the baseline blood sample then your dog has hypothyroidism.

Hypothyroid tests are not 100% accurate. They can be affected by medical conditions, medications, hormones, illness and even the dog's exposure to hot and cold temperatures. When added to information gathered through physical exam, history, and behavior, the tests are a valuable aid in diagnosis.

Treatment of hypothyroidism consists of thyroid hormone supplementation. The most common medication is Levothyroxine, (brand names Soloxine, Synthroid) which is normally given by mouth twice a day. Your vet will want to re-check your dog's thyroid level about six weeks after starting medication. Blood tests will need to be done periodically to make sure your dog's medication remains at a therapeutic level.

A word of caution, as with any medication, your dog can receive more Levothyroxine than it needs. Symptoms of overdose include restlessness, nervousness, excessive drinking and urinating, increased appetite, diarrhea, tremors, cramps, sweating and increased blood pressure and pulse. Symptoms are not always evident right away and may take several days to appear which is why periodic blood tests are so important. Please follow your vets dosing instructions carefully!

Once thyroid supplementation reaches therapeutic levels, you should begin to see improvements in 4 to 6 weeks. An increase in activity levels and mental alertness are among the first changes. Coat and skin changes can take as long as 6 months to return to normal.

Hypothyroidism is a life long illness however, it is easily managed. Once started on thyroid supplementation your dog will need to be on it for life. Medications are not usually expensive and with proper treatment, hypothyroid Shibas will lead a normal life.

Shadow is a 6 year old rescued Shiba who was diagnosed with hypothyroidism at 4 yrs old. He is currently on Soloxine taken twice daily and is monitored through regular thyroid testing. His favorite activities are playing ball, chasing his tail, digging in the garden, hiking, camping, car rides, and playing with the family's other pets!

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