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Endocrine Disorders in Dogs and Cats
Written by Richard Sandore, MD
Produced and edited by Well Beings - Senior Cat & Dog Products. © 2006 WellBeings.com
Reproduced with permission.
The endocrine system is composed of glands that secrete hormones directly
into the blood stream. These hormones regulate and control many of the
body?s metabolic processes. While disorders of the endocrine system are
relatively rare in dogs and cats (with the exception of diabetes mellitus)
they can lead to severe, sometimes fatal disease if unrecognized. Early
identification can many times reduce the need for prescription medications
and some disorders and their associated symptoms are amenable to various
alternative therapies. Additionally, many experts believe that proper diet
and nutrition including high quality supplements can reduce the incidence
of certain endocrine disorders.
In this article we are going to discuss the most common endocrine problems
dogs and cats may face: Hyper- and Hypothyroidism and Hyper- and
Hypoadrenocorticism. Diabetes is covered in depth in a separate article.
What is a Gland?
A gland is a collection of tissue whose function is to secrete hormones
into the blood stream. Each gland secretes one or more unique hormones,
and each hormone has one or more specific functions. Hormones produced by
some glands regulate the production of hormones by other glands. If this
is a little confusing to you, don't worry. We're going to keep things
simple!
The Pituitary Gland
The pituitary gland is located at the base of the brain and is sometimes
called the master gland because it secretes hormones that control and
regulate many of the other glands in the body. If it malfunctions, then
the glands under its control may secrete too much or too little of their
hormones, which then results in symptoms of the particular condition. The
hypothalamus is a part of the brain that secretes hormones that control
some of the functions of the pituitary gland. For our purposes in this
article, that's all we need to know about the hypothalamus.
The Thyroid Gland
The thyroid gland is a single, butterfly shaped structure located in the
neck in front of and alongside the upper part of the trachea (windpipe).
The thyroid gland secretes two major hormones, thyroxine (T4), and
triiodothyronine (T3). The secretion of T3 and T4 from the thyroid gland
is controlled by another hormone, thyroid stimulating hormone (TSH) that
is released from the pituitary gland. The release of TSH is controlled by
still another hormone released from the hypothalamus. Increasing TSH
levels signal the thyroid to release T3 and T4. When TSH levels decrease
the thyroid stops releasing T3 and T4.
Functions of Thyroid Hormones
Thyroid hormones are metabolic regulators and are necessary for the proper
control of many bodily functions. Thyroid hormones assist in the
regulation of digestion, heart rate, skin texture and hair growth, mood,
and maintenance of proper weight. Different sets of problems can arise if
the levels of thyroid hormones are two high or too low.
Hyperthyroidism
Hyperthyroidism is over activity of the thyroid gland. In hyperthyroidism
too much thyroid hormone is produced. The condition usually occurs in cats
older than 7 years, and the average age of occurrence is 13 years.
Hyperthyroidism is relatively rare in dogs, but when it occurs the dogs
are usually older than 5.
Hyperthyroidism is usually caused by a benign tumor in the thyroid gland.
This extra growth of thyroid tissue is not controlled by the normal
feedback system that regulates hormone production and the tumor constantly
secretes thyroid hormones.
The most common sign of hyperthyroidism is weight loss despite an
increased appetite. Other signs are:
- Increased thirst and urination
- Fast heart rate
- Hyperactivity
- Vomiting
- Difficulty breathing
- Poor coat and skin
Hyperthyroidism is usually treated in one of two ways. One treatment is to
surgically remove the tumor. The other treatment is oral administration of
radioactive iodine. The iodine accumulates in the thyroid and destroys all
of the gland, the tumor and normal thyroid tissue. The patient is then
treated with oral replacement of thyroid hormone. Animals (and people) do
very well with this form of treatment.
Hypothyroidism
Hypothyroidism is a decreased production of thyroid hormones. This
condition is very rare in adult cats (unless they have had hyperthyroidism
treated with radioactive iodine). It is, however, a relatively common
disease of dogs. It affects both males and females of any age, though its
incidence increases in older dogs. It is rare in dogs less than 2 years
old. Hypothyroidism is increasingly being recognized as a cause of new
aggressiveness in older dogs.
Hypothyroidism is typically caused by autoimmune destruction of the
thyroid gland. It can also result from decreased functioning of the
thyroid gland associated with aging. The primary signs are fatigue and
lethargy. Other signs include:
- Weight gain
- Weakness
- Exercise intolerance
- Decreased energy
- Hair loss
- Thinning of skin
Conventional treatment of hypothyroidism is oral replacement of thyroid
hormone. If the decreased function is the result of an underlying medical
problem, such as an autoimmune disease, then this must also be addressed.
The Adrenal Glands
The adrenal glands are small, oval shaped structures that are adjacent to
the front of each kidney. Each gland consists of an outer region, the
cortex, and an inner region, the medulla. Three types of hormones are
secreted by the adrenal glands.
Adrenal Hormones and their Functions
The adrenal cortex produces glucocorticoids (for example cortisol) and
mineralocorticoids (for example aldosterone). Glucocorticoids regulate the
metabolism of carbohydrates, fats, and proteins and help the body respond
to stressful situations. Mineralocorticoids are critically important in
regulating salt and water balance in the body.
The medulla produces catecholamines (for example adrenaline). Adrenaline
alters blood pressure and heart rate, and helps prepare the body for
physical exertion or stressful situations.
The secretion of hormones from the adrenal glands is controlled by a
complex interplay between hormones produced by the pituitary gland and
other glands in the body. As with the thyroid, a different set of problems arises from increased or
decreased production of adrenal hormones.
Hyperadrenocorticism (HAC)
Hyperadrenocorticism is the result of excess secretion of glucocorticoids.
It is commonly called Cushing's syndrome. It usually occurs in middle aged
and older dogs, and affects males and females equally. Poodles, small
terriers, and dashunds appear to be predisposed. HAC is uncommon in cats,
but when present usually occurs in middle aged and older cats, and is more
common in females.
The most common cause of HAC is small tumors of the pituitary gland that
secrete excessive amounts of adrenocorticotrophic hormone (ACTH). ACTH is
the hormone that stimulates the adrenal glands to secrete cortisol. Tumors
of the adrenal gland can also directly produce increased amounts of
cortisol. As with the thyroid, these tumors are not under control of
regulatory hormones and produce cortisol constantly.
The most common signs of HAC are increased thirst, urination, and
appetite. These are also the common signs of diabetes mellitus, and in
fact, diabetes is present in 80% to 90% of animals with HAC. Other signs
include:
- Weight loss
- Abdominal enlargement
- Decreased exercise tolerance
- Muscle weakness
- Thin skin
- Hair loss
- Restlessness
Treatment of HAC depends upon the cause; however, in many cases surgical
removal of the adrenal glands with subsequent daily oral replacement of
their hormones is recommended.
Hypoadrenocorticism
Hypoadrenocorticism is a decrease of hormones produced by the adrenal
cortex (cortisol and aldosterone). It is often called Addison's disease.
It is most common in large breed dogs, but is seen with increased
frequency in bearded collies, spaniels, and standard poodles. It is most
common in animals around 3 to 4 years old, but can occur in seniors. The
disorder is relatively rare in cats.
The disease is usually caused by autoimmune destruction of the adrenal
cortex, though damage to the pituitary gland that results in a decrease of
ACTH can also cause Addison's disease. Because cortisol and aldosterone
are critical for maintaining many of the body's regulatory functions,
their rapid decrease can present as an acute emergency with collapse of
the body and unconsciousness.
The disorder, however, usually presents slowly with lethargy, weight loss,
and decreased appetite. Other signs include:
- Vomiting
- Diarrhea
- Increased thirst
- Weakness
Conventional treatment is daily replacement of cortisol and aldosterone.
Summary of Common Endocrine Disorders
The list below summarizes the relative frequency various endocrine
disorders are seen in dogs and cats.
- Hyperthyroidism - Rare in Dogs, Common in Cats
- Hypothyroidism - Common in Dogs, Rare in Cats
- Hyperadrenocorticism - Common in Dogs, Uncommon in Cats
- Hypoadrenocorticism - Common in Dogs, Rare in Cats
- Diabetes - Common in Dogs and Cats
Less Common Endocrine Disorders
There are many other endocrine diseases with a host of causes. These are
rare in dogs and cats and are mentioned for completeness.
Diabetes insipidus is a deficiency of pituitary production of vasopressin
(ADH), or a decrease in the kidneys response to ADH. (This is a completely
different disease than diabetes mellitus, the disorder of glucose
metabolism). ADH is the hormone that signals the kidneys to reabsorb
water. A lack of ADH causes the kidneys to produce large amounts of urine.
The production of urine causes the individual to drink large amounts of
water. Because minerals are also lost in the urine, the blood eventually
becomes dilute and the individual or animal can lapse into a coma and die.
Hyper- and hypoparathyroidism result from abnormal functioning of the
parathyroid glands. The parathyroid glands are attached to each side of
the thyroid and control the level of calcium in the blood.
Acromegaly is caused by an excessive secretion of growth hormone by the
pituitary gland. It results in abnormal enlargement of certain bones and
organs.
Diagnosis
The various endocrine disorders have many signs and symptoms in common.
While a thorough history and physical exam by your holistic veterinarian
is the first step to evaluating any problem, the accurate diagnosis of
endocrine diseases is made by blood tests that measure the levels of
various hormones. As we've seen, the regulation of these hormones is
complex, and sometimes in order to make the diagnosis blood has to be
obtained at set intervals, or at set times after a medication that
stimulates one of the glands is given. You holistic vet will explain in
detail what may need to be done for an accurate diagnosis.
Causes of Endocrine Disorders
While the mechanism whereby an increase or decrease of a hormone leads to
certain symptoms is understood for the disorders we have discussed, little
is known about the underlying causes that lead to over- or underactivity
of the glands. For example, little is known about what causes a pituitary
tumor or an autoimmune attack of the thyroid or adrenal gland.
Though links have not been proven in all cases, many experts find
associations between autoimmune diseases and poor nutrition, environmental
toxins, and food preservatives. These experts stress the importance of
proper nutrition and minimizing the ingestion of chemical and synthetic
preservatives.
Prevention
Unlike diabetes, which can be prevented in most cases with proper
nutrition, diet and exercise, there are no clearcut measures to reduce
the risk of other endocrine conditions. However, proper diet and nutrition
and the use of natural rather than synthetic supplements and preservatives
will boost the immune system and keep the body in the best health
possible.
Alternative Treatments
Alternative treatments for endocrine disorders include herbals, flower
essences, homeopathics, and detoxification. As with any condition, early
recognition and treatment reduces the severity of the disease and assists
any treatment used. Even if conventional medications are necessary for
your companion, the addition of alternative modalities can speed recovery
and reduce unpleasant symptoms.
Herbals
Herbs useful for treating the symptoms of hyperthyroid include bugleweed,
hawthorn, skullcap and valerian. Treatments for the digestive symptoms of
hypothyroid include dandelion root and Oregon grape, and for skin problems
gotu kola, and burdock.
The symptoms of Cushing's syndrome and support of organs affected are
frequently treated with dandelion root, burdock, garlic and nettle. For
support of the adrenal glands in Addison's disease borage leaf and
licorice may be useful.
Herbs that support the immune system include astragalus, garlic, licorice
and Siberian ginseng.
The definitive resource for using herbs to treat our companion animals is,
All You Ever Wanted to Know About Herbs for Pets, by Mary Wulff Tilford
and Gregory Tilford. An incredibly comprehensive review of the history and
uses of herbs, it also has an eye-opening chapter discussing nutrition.
Glandulars
Glandulars are extracts of animal organs, including endocrine glands,
which contain the hormones associated with the gland or organ. Because
glandulars are made from the whole organ they also contain other
substances present in the organ or gland that have not been identified or
isolated. Glandular therapy dates back thousands of years and was used by
the ancient Egyptians and Greeks.
The objective of glandular therapy is to stimulate renewed, vigorous, and
healthy activity of aged or diseased cells through providing natural cell
stimulators found in the tissue of the organ or gland. Even trace amounts
of these stimulators are sufficient to promote the growth of a diseased
gland or organ. Glandulars are powerful preparations and should be used
after consulting your holistic veterinarian.
In Conclusion
The diagnosis of endocrine diseases is complex and requires a trained and
knowledgeable holistic veterinarian who can interpret overlapping signs
and symptoms and complex laboratory tests. While endocrine disorders can
be severe and life threatening, most can be treated safely and effectively
with conventional and alternative treatments. Though long-term medications
are usually necessary, your companion can remain vigorous, healthy, and
active well into their senior years.
Richard Sandore is a medical writer who has practiced allopathic and
alternative medicine. He can be reached at richard(at)richardsandore(dot)com.
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Robbins Pet Care. All Rights Reserved. The products sold by Robbins Pet Care are not intended to be the sole source of treatment or to take the place of expert veterinarian care. Please consult with your veterinarian and ask about using a natural and alternative approach for the treatment of your pet.
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