ROTT N CHATTER, November 1992, Volume 1 Number 4 WHAT'S SO BIG ABOUT THE LITTLE THYROID Part 2 Hypothyroidism is becoming very prevalent in the Rottweiler. Last month I explained how the thyroid is regulated by two different hormones, the Sytimulating Hormone (TSH) and The Releasing Hormone (TRH). I also explained that because of the amount of thyroid hormone a dog needs, hypothyroidism is the disease usually seen whenever there is a thyroid imbalance or malfunction. This month I will touch on the testing for hypothyroidism and the importance of testing ALL of your potential breeding stock. There is a lot of confusion about whether a dog has thyroid disease or not. Most people seem to think that they can tell if there is a problem and therefore only then they should take their dog to be tested. When it comes to the thyroid, nothing can be further from the truth. As thyroid disease develops, it usually starts out as autoimmune thyroiditis. "As what?" you ask. The best way I can explain it is that there are antithyroid antibodies in the blood. In people, this is sometimes referred to as Hashimoto's disease or lymphocytic thyroiditis. The worst part of this is that in 90% of the cases.....it IS genetic! Without testing your breeding stock you won't know it until later when clinical symptoms begin to appear. Tragically this may be after the dog/bitch has been bred and then the predisposition for the disease is passed on to the next generation....and so on....and so on. Let's get to the testing part, since you should now have a basic understanding of T3 and T4. Remember, T3 (triiodothyronine) is the usable thyroid hormone and T4 (thyroxine) has to be converted into T3? The level of these two hormones is not always inter-related, in other words, the dog may show adequate T4 and yet not be producing enough T3, or visa versa. That is oversimplified, but I think you get the idea. Most Veterinarians request only the T4 hormone level that is found in the blood to be measured by their lab. But since there is a tiny amount of T4 hormone that is not in the blood, or "free T4", that is also converted and aids intracellular health, this too should be measured. The only way to know if your dog has thyroiditis and later is a candidate for hypothyroidism is to be sure you ask for a measurement of the total T3 and T4 along with a measurement of the "free T3 and T4". Since studies have shown a definite link between the Cholestrol level and T4 in dogs, your veterinarian should also request a cholestrol level from the SAME blood samples. The results of the testing for cholestrol in relationship to T4 is called the "K" values. With the addition of this test, you may detect early thyroid disease before any clinical symptoms are apparent. Once clinical symptoms appear, the "K" value can aid in identifying whether the dog has low, normal or high thyroid function. If there is no local lab that is familiar with these additional tests, then you may wish to talk to your Veterinarian and have him contact: MICHIGAN STATE UNIVERSITY ENDOCRINOLOGY SECTION ANIMAL HEALTH DIAGNOSTIC LABORATORY P.O. BOX 30076 LANSING, MI. 48909 (517) 353-0621 CLINICAL SIGNS OF HYPOTHYROIDISM ALTERATIONS IN CELLULAR METABOLISM lethargy mental dullness exercise intolerance neurologic signs (polyneuropathy, seizures) weight gain cold intolerance mood swings hyperexcitability stunted growth chronic infections HEMATOLOGIC DISORDERS bleeding bone marrow failure low red blood cell count (anemia) low white blood cell count low platelaet OCCULAR DISEASES corneal lipid deposits corneal ulceration uveitis keraconjunctivitis sicca ("dry eye") infections of eyelid gland (meibomian gland) NEUROMUSCULAR PROBLEMS weakness stiffness laryngeal paralysis facial paralysis "tragic expression" knuckling or dragging feet muscle wasting megaesophagus head tilt drooping eyelids DERMATOLOGIC DISEASES dry, scaly skin and dandruff coarse, dull coat bilaterally symmetrical hair loss "rat tail" or "puppy coat" hyperpigmentation seborrhea or greasy skin pyoderma or skin infections myxedema chronic offensive skin odor CARDIAC ABNORMALITIES slow heart rate (bradycardia) cardiac arrhythmias cardiomyopathy GASTROINTESTINAL DISORDERS constipation diarrhea vomiting REPRODUCTIVE DISORDERS infertility or either sex lack of libido testicular atrophy hypospermia aspermia prolonged interestrus interval absence of heat cycles silent heat pseudopregnancy weak, dying or still born pups OTHER ASSOCIATED DISORDERS IgA deficiency loss of smell (dysosmia) loss of taste glycosuria chronic, active hepatitis adrenal indocrinopathies pancreatic indocrinopathies parathyroid indocrinopathies The above list was graciously provided by W. Jean Dodds, D.V.M. If your dog seems to suffer from any of these ailments, you may want to discuss his/her thyroid with your veterinarian.