hypothyroidism, autoimmune lymphocytic thyroiditis (ALT)—call it
whatever you please—the cause may be slightly different but the symptoms
are the same and very diverse. This is a disease that destroys
thyroglobulin, the portion of the thyroid gland that manufactures
thyroid hormones. It is becoming more common in the Leonberger. In a
health survey done by the Leonberger Club of America in 2000, the Health
Committee found that the disease, which is known to be inherited, occurs
with more frequency in the Leonberger than it does in the general dog
population. Therefore, it is important that owners and breeders learn
as much as possible about the disease.
Thyroid disorders, like ALT, are easy to treat. Twice daily supplements
with levothyroxine sodium, which is a
will bring about recovery. Dogs must be maintained on the hormone
replacement for the balance of their lives. Annual tests are
recommended to make certain their medication dosage is sufficient to
maintain the optimum level.
The OFA has a registry for hypothyroid disease which should be used by
breeders. For more information, visit their website:
The physiologic effects of diminished thyroid
hormones present a remarkable assortment of clinical symptoms. Skin and
coat problems are common; thinning coat and/or hair loss along the
trunk, thighs and tail, and a dry, brittle coat. You may notice breakage
on the neck where the choke chain rests. There may be copious shedding
with only minimal re-growth. Non-itching seborrhea or greasy coat with a
musky odor, pyoderma, folliculitis and skin infections can be present.
Hyperpigmentation or darkening of the skin can be seen in areas with
significant hair loss, while loss of pigment has also been noted in some
The list of symptoms include weight gain and
weight loss, exercise intolerance, muscle weakness, dragging of feet,
head tilting, droopy eyelids and a "tragic" facial expression.
Gastrointestinal symptoms can range from vomiting to diarrhea and
constipation. There may be cardiac abnormalities, low-grade anemia,
changes within the eyes and seizures. Reproductive failures and abnormal
heat cycles are common symptoms.
Weight loss and
hyperactivity can also be symptoms of hypothyroid disease.
Changes and Aggression
In humans, indicators of hypothyroid disease include these symptoms plus
mood swings and behavior changes. Though it opens the door to
controversy, similar symptoms have been noted in dogs. Drs. Jean
DeNapoli, L.P. Aronson and N.H. Dodman of Tufts University, said: "The
mechanism whereby diminished thyroid function affects behavior is
unclear. Hypothyroid patients have reduced cortisol clearance, and the
constantly elevated levels of circulating cortisol mimic the condition
of an animal in a constant state of stress, as well as suppressing TSH
production and thereby further reducing T4 and T3 levels. In humans, and
seemingly in dogs, mental function is impaired and the animal is likely
to respond to stress in a stereotypical rather than a reasoned fashion."
Sudden onset aggression or abnormal responses to stress may be an
indication of a thyroid disorder. In all cases of unexplained aggressive
behavior, a thorough medical history and physical examination should be
conducted, and a complete thyroid panel should be part of any physical.
Testing for the disease is done with a blood test that
includes a “total thyroid panel” TT4, TT3, FT4, FT3, TSH and TgAA).
New tests have been developed in the last decade but accurate diagnosis
is not always easy. The levels of thyroid hormones circulating in the
blood vary throughout the day and are affected by many variables.
Natural biorhythms, estrous, and pregnancy cause hourly fluctuations.
These highs and lows are normal for the individual dog. Testing the
blood measures the levels of thyroid hormone circulating when the blood
is drawn. Adding to the difficulties of accurately assessing thyroid
function, laboratories throughout the country have different values.
Too many veterinarians consider a serum T4 alone as a diagnostic test
for thyroid disease but experts do not consider this single test to be a
precise measurement of thyroid function.
The best indicator of the disease is a positive TgAA test
result. Early testing for the presence of autoantibodies to
thyroglobulin, T4 or T3 is very important if we are to reduce the
incidence of disease in the breed. The majority of dogs that develop
autoantibodies will test positive as early as one year of age, and
typically as young adults (three to four years old), will eventually
develop symptoms. Keep in mind that the presence of autoantibodies at
any time in the dog's life is an indication the disease is the heritable
form. Dogs that are negative at one-year of age may become positive at
five or six years of age. Until a specific genetic test is available,
TgAA testing is necessary. Dogs should be tested every year or two in
order to be certain that they have not developed the condition. Since
the majority of affected dogs will have autoantibodies by four years of
age, annual testing for the first four years is recommended. After that,
testing every other year should suffice.
After instituting initial hormone supplementation, it will
take several weeks to a month before clinical signs of hypothyroidism
begin to resolve. Severe skin and coat abnormalities may take longer. Follow-up
testing is imperative, usually after six to eight weeks, to determine
the effectiveness of the dosage. The sample should be drawn four to six
hours after the morning pill. Subsequently, thyroid levels should be
monitored annually with complete thyroid testing to check levels and
make sure the body is converting the T4 hormone into T3.
(C) Copyright 2002 Barbara Bouyet