The thyroid gland controls the metabolic rate of all the organs. If it is under-active, a dog can have one, or many, of these:
1) act sluggish (lethargic, quiet)
2) slow heart rate
3) have hair loss which is "bilaterally symmetrically" ie. each side of the dog's hair loss pattern matches the other side. The hair loss is usually along the back of the dog.
4) "rat tail" appearance to the tail.
5) overweight or obese
6) anemia - low red blood cell count
7) chronic or intermittent ear infections.
8) elevated cholesterol
9) elevated liver enzymes (ALT or SAP)
10) Aggression or other behavior issues
11) Less common manifestations include eye and nervous system diseases; paralysis of the larynx (laryngeal paralysis); or enlarged esophagus (megaesophagus).
As with most diseases, these symptoms may not be just seen with hypothyroidism. Remember, Veterinary Medicine is not an exact science. For example, allergies, parasites (fleas, scabies, demodex, etc), Cushings (adrenal gland dysfunction), and many other ailments can cause a pet to have hair loss. Overfeeding can cause a pet to be overweight, etc.
The most common breeds that tend to be prone to Hypothyroidism:
There are different tests that can be used to test for hypothyroidism. There are times when screening tests are done, and confirmation tests need to be added on. Some pets will have part of the thyroid panel abnormal, but other parts will be normal. There may be something on screening blood work that may give your Veterinarian reason to believe that you pet may be hypothyroid. For example some enzymes, such as SAP or ALT, and cholesterol may be elevated on the blood work, which could indicate hypothyroidism.So, it is not as simple as just picking one test and having that be abnormal. Multiple tests may need to be done. If hypothyroidism is ruled out as a possibility, then your Veterinarian may need to look into other possibilities for your pets symptoms.
Once a diagnosis is made of hypothyroidism, your pet will be put on medication that they will stay on life-long. Since each animal is an individual, the dose of the medication may need to be adjusted. I generally recheck the thyroid level a month after starting the thyroid medication. If it is still low, the dose will be adjusted, and the level rechecked in a month. If the thyroid level is OK, then the level should be rechecked every 6 months. Remember, individual variations do exist, so please follow your Veterinarians recommendations. Most Veterinarians will require that the recheck thyroid levels be tested 4-6 hours after the medication was given.
If you would like to read more, I recommend Dr. Jean Dodds book, " The Canine Thyroid Epidemic: Answers You Need for Your Dog"
This blog is informative only, and should not be used to replace a Veterinarian's evaluation. The article included Cynthia Mazzola DVM's opinions based on more than 20 years of practicing Veterinary Medicine. Remember: there is more than one way to do things, and they could both be correct.