Hypothyroidism is caused by a thyroid hormone deficiency in the body. People suffering from low thyroid levels may feel sluggish or gain weight easily. The same holds true in dogs. But affected dogs may display other symptoms because the thyroid hormone, known as thyroxine, affects just about every organ in the body.
Hypothyroidism most often occurs when a dog's immune system destroys its thyroid gland, which is located just below the throat. This condition is called autoimmune hypothyroidism. In other dogs, the thyroid gland wastes away, and the cause is unknown. Occasionally, hypothyroidism is present at birth and leads to a form of dwarfism.
Risk factors and detection
Middle-aged dogs are at higher risk for autoimmune hypothyroidism, and females are twice as susceptible. Breeds that are predisposed to this condition include golden retrievers, cocker spaniels, Labrador retrievers, Doberman pinschers, Miniature schnauzers, Irish setters, Poodles, Dachshunds, Boxers, Great Danes, Shetland sheepdogs, chows, English bulldogs, Airedales, Pomeranians, and Old English sheepdogs.
No particular breed or gender is linked to the rare congenital form of hypothyroidism, which prevents normal development. Affected dogs are much smaller than their littermates, have large heads and short legs, and usually maintain their puppy haircoat. Avoid breeding dogs with any form of hypothyroidism because the condition may be hereditary.
Signs of hypothyroidism include:
- weight gain without an appetite increase
- lethargy
- constipationnon
- itchy hair loss, which is usually confined to the sides or tail
- poor hair regrowth after shaving
- dry, brittle haircoat
- dark or flaky skin
- recurrent ear or skin infections (the latter can be itchy in some cases)
- reproductive problems in unspayed females, such as absent or irregular heat cycles
- nerve and muscle abnormalities, such as facial paralysis
- voice change
- vomiting
- knuckling under of the toes or dragging of the feet.
As you can see, the symptoms vary. Not all of these signs must be present, and any of these symptoms could be caused by other conditions. How's that for confusing?
To diagnose the condition, your veterinarian will perform a thorough physical examination of your dog. The doctor may discover subtle problems you didn't notice, including a low heart rate, a low body temperature, dry eyes, deposits in the cornea, or slowed reflexes.
Your veterinarian also will consider other conditions that may cause similar symptoms. Some examples: Cushing's syndrome (hyperadrenocorticism) or sex hormone tumors may cause bilateral, nonitchy hair loss. Addison's disease (hypoadrenocorticism) or a heart abnormality may cause a slowed heart rate, lethargy, and weakness.
As part of a complete examination, the doctor also will take a sample of your dog's blood to test the levels of thyroxine (T4) and thyroid stimulating hormone (TSH). Abnormalities may include a low T4 level, a high TSH level, mild anemia, and a high cholesterol level. Your veterinarian also will rule out concurrent problems that falsely lower a dog's thyroxine level.
Prevention and treatment
There is no known prevention for hypothyroidism, but treatment generally produces positive results. Dogs receive thyroid supplementation (synthetic L-thyroxine) in pill form, usually twice a day for life. Your veterinarian usually will take a blood sample six to eight hours after the first dose. If the dose is too high, such signs of hyperthyroidism as panting, nervousness, increased thirst and urination, and increased appetite can occur. These symptoms resolve quickly once the doctor adjusts the dose.
Your veterinarian will monitor your dog's thyroxine level periodically—usually within six to eight weeks after starting therapy, again a few weeks after making any dose changes, and once or twice a year to ensure the dose is adequate.
Your dog's energy will return about a week after treatment begins. You'll notice improved skin and weight loss in four to eight weeks, and hair will regrow fully in several months. Dogs treated for hypothyroidism typically live a normal life with continued therapy.
