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Dog Health Questions: A Vet's Advice About Canine Hypothyroidism
What the Vet Says About Canine Hypothyroidism
Dr. Cathy Alinovi of Hoofstock Veterinary Service recently agreed to spend some time with me discussing canine hypothyroidism, which is one of the most common disorders of the endocrine system seen in dogs.
Early detection and treatment are crucial to prevent other health problems from developing.
As a holistic veterinarian, Dr. Cathy utilizes a whole body approach that considers all contributory factors as she works with her clientele to provide emergency and preventative care services.
In addition to operating her veterinary practice, she and Susan Thixton are co-authors of the book Dinner PAWsible, which is a convenient guide for owners to a wide range of recipes for making tasty and nutritious meals for their cats and dogs.
In today's interview, she offers her answers to some common questions that owners have about their pet's condition, treatment options, and prognosis.
Definition of the Disease & Important Terminology
Donna Cosmato (DC): Please define canine hypothyroidism in plain English for readers.
Dr. Cathy: “Hypo” means low, thus hypothyroidism means low thyroid levels. When hypothyroidism is the diagnosis, the traditional assumption is the patient has low thyroid hormone (called T4) production. Interestingly, humans with thyroid problems usually have hypothyroidism, too. To understand canine hypothyroidism fully, we need to define some terminology first.
T4 is the hormone most people talk about when they discuss thyroid function. T is for thyroid hormone, but it is also for tyrosine, the amino acid on which the hormone is based. Four means there are four molecules of iodine attached to the hormone. Proteins in the blood carry T4.
T3 is the active form of thyroid hormone, and it is what all the cells in the body use to determine their rate of activity (which is also called the metabolic rate). One iodine is removed from T4 to make T3.
Free T4 and free T3 are the hormones in the blood not attached to transport proteins.
TGAA is thyroglobulin autoantibody. This is a by-product of an autoimmune breakdown of the thyroid gland.
TSH stands for thyroid stimulating hormone. TSH is made in the pituitary gland, which is located at the base of the brain, back between the eyes. The pituitary measures levels of circulating thyroid hormone to decide how much more the body needs. The pituitary produces TSH, which is sent to the thyroid gland; the thyroid gland then produces T4.
Sick euthyroid – “eu” means normal, so when a patient is sick, their thyroid will under-function, but it is a normally functioning thyroid gland. However, a blood test performed while the patient is ill will reveal low levels of circulating T4. When the patient returns to health, the T4 levels will also return to healthy levels.
Causes of Canine Hypothyroidism
DC: What causes hypothyroidism?
Dr. Cathy: The main causes of hypothyroidism include low dietary sources of iodine, selenium, tyrosine and other vitamins and minerals or autoimmune breakdown of the thyroid gland. There can also be problems at the pituitary, which cause reduced production of TSH.
DC: What clinical signs should owners watch for?
Dr. Cathy: Be alert for any increase in weight, dry coat hair, patches of skin without fur, and reduced energy. Other signs might include a pendulous abdomen (potbelly) or skin infection and anemia (low blood count). I have seen dogs that are just plain overweight, but no matter what the owner tries for weight control, they were hypothyroid. I also treated one little dog, who was a bit chubby, who had chronic anal gland issues.
These clinical signs occur because of weakened body systems. The anemia develops because the bone marrow is not stimulated to make red blood cells. Thus, potbelly happens because the protein leaks out of the blood into the abdomen, and the muscles are weak due to a lack of thyroid hormone. Skin or anal gland infection occurs because the immune system is not stimulated optimally by the thyroid hormone, thus infection sneaks in.
Types of Canine Hypothyroidism
DC: How many types (or degrees) of hypothyroidism are there?
Dr. Cathy: Sick euthyroid, as we discussed previously, occurs when the body is ill. Everything, including the thyroid gland’s function is affected; therefore, T4 production is low. As soon as the primary illness is fixed, so is the T4 production. This is the first reason why measuring T4 alone is not accurate.
Low T4: This can be as simple as not enough iodine present to add the 4th iodine (thus the 4 in T4).
Low T3: This can be a conversion problem where the body cannot remove an iodine molecule. Since the body uses T3, if the body cannot convert T4 to T3, there is a relative deficiency of thyroid hormone even if T4 measures normally in the blood screen in the vet’s office. This is another reason why measuring T4 alone is not an accurate test.
Autoimmune destruction of the thyroid gland: Known as Hashimoto’s disease in humans, this is a fourth type of thyroid disease. While we think of autoimmune disease as affecting the whole body, in reality, many autoimmune diseases affect just one organ, such as the thyroid gland. Something causes the thyroid gland to destroy itself, and while these factors are not well known, in humans there are links to cigarette smoke; gluten and food allergies; too much iodine or too little selenium in the diet; and previous illness.
Pituitary: Another type of thyroid disease is caused by low pituitary function. The pituitary is the master gland, and it sends signals to most of the other glands in the body including the thyroid, the adrenals, the ovaries, and the testes. Commonly, in older patients, a tumor is responsible for low pituitary function. If the pituitary does not signal the thyroid gland to function, thyroid hormone levels will be low.
DC: What are the most common contributing factors?
Dr. Cathy: Any incidence of inflammation and poor nutrition can be a contributing factor. Poor nutrition is a bit of a misnomer as it can be that the food contains adequate nutrition, but the body cannot absorb it. Some may ask why the body would not absorb vitamins and minerals. Either the nutrients are not in an absorbable form, as in the case of many synthetic vitamins added to pet foods, or the intestines contain so much inflammation that they cannot absorb any nutrients. These causes of inflammation can be other infection, allergies or “leaky guts.”
Special Needs Groups
DC: Are there canine populations that are at a higher risk?
Dr. Cathy: Yes, those groups would be Doberman Pinschers, Golden Retrievers, Great Danes, Irish Setters, Boxers, and Dachshunds. However, any dog can be hypothyroid.
DC: How is hypothyroidism diagnosed?
Dr. Cathy: Diagnosis is made via a blood test. However, there are some important things owners need to know. Traditionally, and most commonly, a “screening” test only measures T4 levels. T4 can be low when the patient does not feel well (sick euthyroid); therefore, measuring T4 alone is not an accurate test. To diagnose hypothyroidism properly, the blood sample should go to a laboratory that tests for T3, free T3, T4, free T4, and TGAA (thyroglobulin autoantibody). Hemopet and a few other laboratories provide complete thyroid testing.
DC: What are the most common treatment methods?
Dr. Cathy: Normally, thyroid replacement hormone is given but this can be tricky. Because of the way the feedback from the body goes to the thyroid gland and pituitary, if thyroid replacement hormone is given, the body is fooled into thinking that there is enough available so it sends a signal to the thyroid gland, via the pituitary, that it doesn’t need to make more thyroid hormone. This becomes a vicious cycle.
If the real need is for more selenium (for example), a nutritional supplement can make the thyroid gland function optimally on its own. However, if the thyroid gland is completely destroyed, as it is in autoimmune thyroid disease, supplementation with thyroid replacement hormone is the most appropriate thing to do.
DC: Are there any natural remedies used for treatment?
Dr. Cathy: One natural remedy is to feed the glandular tissues by feeding thyroid gland, plus or minus pituitary gland, in a tablet. Other natural remedies include supplementing with the missing nutrient like iodine or selenium. Interestingly, if stomach acid production is low, the body will not make tyrosine efficiently; tyrosine is an amino acid, which comes from protein, like meat. Tyrosine is the backbone of T3 and T4 (tyrosine is the T). Something as simple as making sure there is sufficient stomach acid production can be useful; therefore, digestive enzymes are beneficial.
Eastern medicine also treats hypothyroidism through a process of determining the underlying pattern of illness to identify the contributory cause. Next, the pattern is treated with herbal therapy.
Potential Adverse Reactions
DC: Are there any known side effects or negative reactions to the treatment methods?
Dr. Cathy: Over supplementation with thyroid hormone can lead to hyperthyroidism, which is a condition where the dog loses weight in spite of eating a lot. This is why retesting is so important (in this situation, it’s fine to screen for T4 levels). In unusual cases, dogs are allergic to the dye used to color the thyroid supplement tablets; I have seen two such dog patients in my practice.
Pallative Treatments & Prognosis
DC: What can owners do to make their pets more comfortable?
Dr. Cathy: Feed a high quality food based on meat that is preferably an unprocessed food, so the nutrients come directly from the food and do not have to be supplemented by the pet food manufacturer.
DC: What is the prognosis for a dog with canine hypothyroidism?
Dr. Cathy: Prospects are good when the disease is properly diagnosed and treated accordingly.
DC: What have I forgotten to ask you that my readers might want to know?
Dr. Cathy: A diagnosis of thyroid disease is rarely a reason to panic. What is important to know is how the diagnosis was made; for instance, was a thorough test performed? A diagnosis based on T4 levels alone is not a true diagnosis. The patience to determine the underlying cause of hypothyroidism in a doggy patient provides the best treatment for the dog’s best quality of life.
In humans, Hashimoto’s is the most common cause of hypothyroidism. However, this is not the case in dogs. Because the thyroid gland is destroyed in Hashimoto’s, humans have little alternative other than to supplement their missing thyroid hormone. Since there are many more reasons for dogs to have hypothyroidism, it’s important to identify the underlying cause and treat the condition appropriately.
I have “cured” several hypothyroid dogs through nutrition. These dogs were sick euthyroid and needed their “leaky gut” treated. Once that was fixed and the nutrients were absorbed – walla! Normal thyroid levels!
Telephone interview with Dr. Cathy Alinovi, 02/19/2012
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