GENETIC HEALTH – Hypothyroid Part II
By Sharon Schaefer
As stated in the first article, accurate diagnosing of thyroid dysfunction in dogs is not as simple as in people. The veterinarian needs to consider a blood panel to eliminate other possible illnesses as well as careful interpretation of three to six thyroid functions, including Free T4 checked through equilibrium dialysis and not a less reliable method. Prebreeding screening should include TgAA.
The dog should be tested at least 90 days after vaccination, when it is not on any other medications, and 12-16 weeks after the start of the last heat cycle in females. Dogs with TgAA present should not be bred from and should be retested in 6 – 12 months as this could be the earliest indicator of a thyroid problem. If the retest is negative for TgAA, and the other thyroid functions are still normal, the dog is a candidate for breeding. In families with known hypothyroid the recommendation is to do a full thyroid function test annually until age three before breeding.
Dogs which are symptomatic and confirmed hypothyroid as above should be treated with levo-thyroxine a synthetic thyroid hormone. The dose should be split, 12 hours apart, morning and evening and preferably not given with food (especially on blood test day). Dr. Jean Dodds, supported by an increasing amount of recent clinical evidence, also recommends treating those with consecutive tests showing rising TgAA. Since about 75% of the thyroid gland needs to be destroyed before a dog may show significant symptoms, treating at the first clear blood test indication of hypothyroid avoids significant trauma. Maintenance levels of thyroxine are then lower.
Given an appropriate dosage of thyroxine, the dog with symptoms of lethargy, heat seeking, or mental conditions should show improvement in less than two weeks. Changes to skin, coat, and weight will be a slower process taking two to three months. Hair loss might get worse a few weeks after starting treatment. Blood levels (total T4 and TSH or T4 and FreeT4) need to be checked in 6-8 weeks for dose adjustment. The blood test needs to be done close to 6 hours after the morning dose of thyroxine.
If symptoms are not responding then blood levels should be checked sooner and elimination of all other possible disease conditions reconsidered. After every dose adjustment, blood levels will need to be retested in about 2 weeks to ensure ongoing appropriate correction of the problem. For maintenance many dogs are fine with a single morning dose and complete thyroid retests every 6 or 12 months.
References
www. upei.ca/cidd/intro.htm
www. itsfortheanimals.com Click: Dr. Dodds/HEMOPET
www.ofa.org
www.pubmedcentral.nih.gov Search: canine hypothyroidism
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