Thyroid Dysfunction, 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 hormone replacement, 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:

http://www.offa.org/thyinfo.html

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 Leos.

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.

Mood 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