Hypothyroidism is a clinical state associated with
inadequate production of thyroxine (thyroid hormone), which causes lowered
cellular metabolism in most tissues of the body. The most common form in the dog is
primary hypothyroidism 95%, which results from significantly decreased hormone
production by the thyroid gland due to an inflammatory disease or simple loss of
function. Clinical signs usually develop during middle age (4 to 10 years).
They tend to occur at an earlier
age in breeds at increased risk including Golden Retrievers, Doberman Pinschers,
Dachshunds, Irish Setters, Schnauzers, Great Danes, Poodles, and Boxers.
The signs vary and depend in part on the age of the
animal. In adult dogs, the most consistent clinical signs of hypothyroidism
result from decreased cellular metabolism and its effects on the animal’s mental
status. Most show some mental
dullness, lethargy, exercise intolerance or unwillingness to exercise, a
propensity to gain weight without an increase in appetite or food intake, and
cold intolerance. These signs are often gradual in onset, subtle, and not
frequently recognized by the owner until questioned by a veterinarian.
Additional indications typically involve the skin and, less commonly, the
neuromuscular system.
Dermatologic alterations include hair loss on both
sides of the body that tend to spare the head and extremities. It may be` localized or generalized and
can involve only the tail (“rat tail”).
Seborrhea (dry or oily skin) and pyoderma (skin infection) are also common signs. Lastly, the hair
coat is often dull, dry, and easily pulled out. Hair regrowth is often very slow. Chronic ear infections have also been
noted. Less common manifestations include eye, cardiovascular, and
gastrointestinal abnormalities.
Hypothyroidism is relatively easily treated and
routinely diagnosed with blood chemistries. Occasionally, additional testing may
be required to accurately diagnose the condition. The treatment of choice is
daily synthetic thyroid hormone supplementation in the form of tablets. Once an animal is started on
supplementation, improvement in activity and attitude is usually noted within
7-10 days. Visible improvement in
skin and hair coat may take 6-8 weeks or longer. Follow-ups include rechecking thyroid
levels 4-8 hours post-pill in 3-4 weeks. Frequently, the dosage may need to be
changed and rechecked during the first 3 months of treatment. Once the proper dose is identified,
lifelong administration is required with periodic thyroid level checks 1-2 times
yearly.
-----------------------------------------
