Hypothyroidism By Dr. Ed Mapes Stonebridge Animal Hospital McKinney, TX

Vet McKinneyHypothyroidism: the signs can be so obvious in some and so difficult to recognize in others.  Thyroid hormone controls the body’s metabolic rate; low levels cause a slowdown of that rate.  Metabolic rate controls activities in all body systems, so clinical symptoms can reflect a wide range of abnormalities.  Symptoms, therefore, can be different in each patient.  Energy levels, skin and hair coat problems, weight gain, poor immune response to infection, delayed wound healing, and problems involving the heart, muscles, reproductive system, and intestinal tract relate directly to hypothyroidism.

The most common symptoms include obesity, low energy levels, feeling cold that causes heat seeking, hair loss that is usually not associated with scratching, and “mental dullness.”  Some patients can be identified by the look on their faces relating to skin changes that cause puffiness around the eyes and sagging lids: the so-called “tragic” face.

Through examination, vets in McKinney can discover below-normal heart rates, thickened skin, and masses at the tail head area. Common signs of hypothyroidism include: dryness of the skin and hair, excessive shedding and poor hair growth rates causing hair loss (alopecia) that is often bilaterally symmetric over the neck, trunk, caudal thigh region, and tail.  Impaired immune response to infection often leads to bacterial or yeast skin infections that cause skin sores, scratching, and odor.  Routine blood testing may show no abnormalities or slight anemia.

Vets in McKinney see many cases without the classic symptoms mentioned above, so diagnosis depends on a “high index of suspicion” by the veterinarian; in other words, we must be aware that hypothyroidism can be involved, even without the normal signs.

Especially during the spring and summer months, we see patients that exhibit itching and skin lesions that are not controlled with the usual medications to control allergy.  Testing discloses decreased thyroid function, and the skin lesions disappear when thyroid status is improved with medication.

Blood testing for hypothyroidism can also be difficult to interpret; low levels of thyroxin (thyroid hormone) can be the result of other chronic disease processes.   The body responds to those diseases in a number of ways, one of which is to decrease the metabolic rate by suppressing thyroxin release.  In these circumstances, decreased thyroid hormone levels actually indicate secondary hypothyroidism, and supplementing with thyroid hormone will not correct either the low thyroid levels or the primary disease process. Common diseases causing secondary hypothyroidism are kidney disease, Cushing’s syndrome, chronic allergic dermatitis, and Addison’s syndrome.

Thyroid testing must be tailored to ensure accurate diagnosis (whether we’re faced with true hypothyroidism or a secondary case).  Therefore, when attempting to diagnose a case for the first time, I usually send a blood sample to the reference laboratory that can assay for the following constituents:

-T4: Thyroxin that is bound to protein in the bloodstream, and may not be available to stimulate cells.  T4 levels can be affected by other drugs, illness, or other changes within the body.  Thyroxin levels are therefore not always accurate indicators of thyroid states.  We test for T4 at the hospital, but reserve that testing for cases that are already diagnosed as hypothyroid.

-Free T4: The active (unbound) form of the hormone that is available for uptake by body cells to govern their actions.  This form of thyroid hormone is the better reflection of hormonal status.

-TSH: Thyroid Stimulating Hormone is produced by the pituitary gland in the brain.  It is part of the body’s feedback system to maintain normal thyroid status.  Low levels of T4 and free T4 cause the pituitary to produce TSH, which stimulates thyroid production by the thyroid glands.  Elevated TSH indicates hypothyroidism while suppressed TSH can be seen in secondary hypothyroid or in hyperthyroid cases.

This complete thyroid testing helps vets in McKinney to more accurately assess the thyroid state because multiple parameters are available.  It is not uncommon to see decreased T4 combined with normal levels of free T4 and TSH – the classic secondary hypothyroid situation.  This is an alert that searching for a hidden illness rather than treating for low thyroid levels is what the patient needs.  Thyroid levels usually return to normal status when the primary illness is addressed.

Diagnoses of true hypothyroidism call for supplementation of thyroid hormone via either pills or chewable tablets.  I usually initiate therapy at a given dosage and then re-assess thyroid levels after one month of therapy.  We perform this recheck testing (of T4 only) in the hospital, which takes only minutes.  An adjustment of the medication dosage is sometimes required based on that test.

Patients must receive thyroid replacement for life after we determine the proper dosage.  Levels should be rechecked on a yearly basis, since requirements can change over time.  With hypothyroidism, the trick is to recognize even subtle symptoms so as not to miss the condition, to avoid false diagnoses when levels are depressed due to another disease process, and then to prescribe the proper dosing levels of replacement hormone for the patient.

Vet McKinney
Stonebridge Animal Hospital
5913 Virginia Parkway
McKinney, Texas 75071

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