“Cats are not small dogs” is a saying the head DMV at my local veterinary hospital would often quote when talking me through different conditions we would see in our feline patients. This conundrum is perfectly exemplified by differing conditions of the thyroid seen in cats versus dogs, a well-documented, chronic endocrine disorder. While the exact cause and pathogenesis of the development of hyper- and hypo- thyroidism in cats and dogs is still blurred, what is abundantly known is the persistence of hyperthyroidism in cats and hypothyroidism in dogs with the opposite conditions (hyper- in dogs and hypo- in cats) being exceedingly rare in felines and canines.
Hyperthyroidism is characterized by overactive and enlarged thyroid glands. It is caused by an increase in the hormones tetraiodothyronine (T4) and triiodothyronine (T3) which are integral to metabolism and normal bodily functions. A T4 and TSH blood chemistry paired with observations of increased appetite and thirst, swift weight loss, increased urination, and elevated resting heart rate can indicate hyperthyroidism in a patient; indicative of the oxidative stress and antioxidant imbalances of the metabolism hormones kicked into ‘overdrive’. Treatments include 1) the medication methimazole, an enzyme inhibitory drug affecting the patient’s ability to synthesize T3 and T4 hormones, 2) a bilateral thyroidectomy, removing the overactive thyroid glands, and 3) radioactive I-131 treatment which affects the transfer of iodine to the necessary hormone precursor of T3 and T4.
Hypothyroidism, in contrast, is characterized by extremely low levels of the tetraiodothyronine (T4) and triiodothyronine (T3) thyroid hormones. A T4 and TSH blood chemistry paired with observations of rapid and extreme weight gain, muscle loss, increased lethargy/sluggishness, and decreased resting heart rate help in a correct diagnosis of hypothyroidism; slowing metabolism dramatically. Treatments include levothyroxine, a hormone drug that acts to compensate for the loss of T3 and T4 in the body.
Hyperthyroidism in dogs and hypothyroidism in cats is beyond rare, and if seen, is most often the result of high dosages in treatment. Careful and regular blood chemistries are necessary for evaluating and prescribing the correct dosage to achieve the desired balance for hormone inhibition or hormone compensation. I think this is an interesting example of how medications have the potential to restore homeostasis or tip the scales in reverse effect.
I had a very difficult time finding sources on causation for the difference in disease pathology in canines and felines in relation to the thyroid. I think this speaks towards the growing gap in new research in the veterinary and medical fields.
Hey Hannah!
ReplyDeleteI loved your article, as it was both very well written and stated the facts rather than including unnecessary and irrelevant information. As someone who wants to go into the medical field, rather than veterinary medicine, is there any correlation in the hypo- and hyper- thyroidism biochemistry or treatment as compared to that in humans? I also know that levothyroxine is a very often prescribed medication given to humans for hypothyroidism but was also wondering if its targets are the same in humans as in animals? Another question I had for you is, has the trend in the prevalence in endocrine system related disorders in humans also been mirrored in animals, and how may that correlate to the increase in additives and preservatives being found more frequently in both human and animal food sources? Overall, you did a great job and definitely sparked an interest in me as to how veterinary medicine can often times mimic human medicine.