Addison's Disease

Introduction | Causes & Prevention | Symptoms & Signs | Diagnosis & Test | Treatment Options

Addison's Disease

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Introduction

Addison's Disease, technically called hypoadrenocorticism, is defined as inadequate production of corticosteroid hormones by the cortex (outer part) of the adrenal glands. The adrenal glands are paired organs, located in the abdomen next to the kidneys, which produce and regulate a number of endocrine hormones that are essential to normal body function. The adrenal glands can be damaged in a number of ways, including by trauma, toxic drugs or chemicals, cancer, immune-mediated disorders and infection, among others.

An acute Addisonian crisis can be caused when corticosteroid drugs that have been administered for some other medical condition are abruptly withdrawn. While the dog is receiving the steroids, its adrenal glands go into a type of resting state. When the external steroids are stopped, the dog can develop a temporary but serious shortage of adrenal hormones, which can quickly lead to shock and cardiovascular collapse.

An Addisonian crisis is a true medical emergency. Most experts agree that approximately 90% of the adrenal cortex must be damaged or destroyed before a dog will show observable signs of Addison's Disease. This is not a common condition in domestic dogs, but if left undiagnosed or untreated, Addison's can be life-threatening. This is primarily due to elevated potassium levels (hyperkalemia) and low sodium levels (hyponatremia), which can cause serious dehydration, blood volume depletion and severe problems with the heart and other organs. Addison's Disease can't be cured. Fortunately, if caught early enough, it usually can be controlled.

Causes & Prevention

Causes of Addison's Disease
Veterinarians are not always able to determine the exact reasons why their canine patients developed Addison's Disease. In the most general sense, Addison's is caused by some injury to the adrenal cortex, which is the outermost part of the paired adrenal glands, which are located next to the kidneys. The cortex is made up of three separate layers: the external zona glomerulosa, the middle zona fasciculata and the innermost zona reticularis. The adrenal cortex is responsible for producing, releasing and regulating three main groups of hormones: glucocorticoids, which deal with maintaining proper levels of glucose in the bloodstream; mineralocorticoids, which help maintain appropriate levels of circulating electrolytes; and androgens, which have masculinizing effects similar to those of testosterone. The other anatomical part of the adrenal gland is the medulla. The adrenal medulla is the innermost part of the adrenal gland and is primarily responsible for producing, releasing and regulating the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline).

In most cases, Addison's Disease results from the wasting away of one or more layers of the cortex of one or both adrenal glands. This can be caused by a number of different things, some of the more common of which are auto-immune disorders. Auto-immune disorders occur when a dog's complex, finely-tuned immunological system malfunctions and starts to attack the tissues of various parts of its own body – in this case, the adrenal glands.

Other things that can damage the adrenal glands include overdoses of certain medications, long-term administration of corticosteroid hormones, trauma or other physical injury to the adrenal glands, adrenal tumors or cancer, and granulomatous disease, which is a disease that involves formulation of tumor-like masses of granulation tissue. Ultimately, anything that damages the adrenal glands' ability to produce a normal quality and quantity of corticosteroid hormones can contribute to Addison's Disease in companion dogs.

Prevention of Addison's Disease
There is no fool-proof way to prevent Addison's Disease in dogs, since the exact causes of this ailment are still unclear. Of course, preventing abdominal trauma can prevent physical injury as a cause of adrenal gland damage.

Special Notes
If left untreated, or if diagnosis is delayed for too long, Addison's can be fatal. When there are not enough adrenal hormones circulating through a dog's bloodstream, the levels of potassium, sodium and chloride can quickly become imbalanced. This, in turn, can cause rapid and severe dehydration, depletion of normal circulating blood volume and significant problems with the animal's heart and other vital organs. This is called an "Addisonian crisis." A dog in an Addisonian crisis must be hospitalized and treated immediately and aggressively to have a realistic chance of pulling through. The prognosis for dogs with Addison's Disease is usually very good, if the condition is caught and treated early in its course. Unfortunately, diagnosis can be difficult, because most of the outward signs of Addison's are nonspecific and can mimic those of many more common canine ailments.

Symptoms & Signs

How Addison's Disease Affects Dogs
Addison's Disease is an endocrine disorder caused by inadequate production of corticosteroid hormones by one or both of the dog's adrenal glands. The symptoms of this disease typically wax and wane, which means that they come and go, and they can range from mild to extremely severe and can vary over time. Dogs with Addison's tend to feel lousy in waves, especially when they are under stress. They may experience belly pain, nausea, vomiting, diarrhea, weakness, depression and other unpleasant symptoms of systemic illness.

Symptoms of Addison's Disease
While the signs of this disease are fairly non-specific and can be caused by a number of different disorders, most watchful owners usually can spot the signs of Addison's in their dogs, even though they may not know what is causing them to occur. Outward signs of Addison's in dogs usually include one or more of the following:

weakness
lethargy
lack of appetite
vomiting
regurgitation
diarrhea (with or without blood)
weight loss
Poor skin and coat condition
abdominal pain
increased thirst (polydypsia)
increased urination (polyuria)
shaking, trembling, shivering
collapse
shock
Another potential sign of Addison's Disease is when a dog unexpectedly deviates from its normal activities or routines, for no apparent reason. For instance, if a dog is reluctant to jump on a couch or bed that it usually leaps on happily, the owner should pay attention, because pain and muscle weakness can accompany Addison's Disease and could be contributing to the dog's discomfort. All of the above signs are commonly associated with other conditions. However, the symptoms of Addison's usually become more frequent and severe over time, as the dog's body becomes increasingly damaged from the effects of the disease. One of the hallmarks of Addison's is that the signs worsen with stress. By the time a dog is diagnosed with this disease, emergency medical treatment normally is necessary. Once a dog has been stabilized, the attending veterinarian can make a proper assessment of its condition and status, and proper treatment protocols can be implemented.

Predispositions
Addison's Disease is most commonly seen in young to middle-aged female dogs averaging between 4 and 6 years of age, although dogs of any age or gender can be affected. It is not entirely clear whether there are definitive breed predispositions for this disease. However, some authorities suggest that Great Danes, West Highland White Terriers, Bearded Collies, Standard Poodles, Rottweilers, Basset Hounds, Labrador Retrievers, Nova Scotia Duck Tolling Retrievers, Leonbergers, Soft Coated Wheaten Terriers and Portuguese Water Dogs are at an increased risk. Because of this, a genetic component is strongly suspected.

Diagnosis & Tests

Initial Evaluation
Addison's Disease can be difficult to diagnose because it is relatively uncommon in dogs, and also because its symptoms mimic those of many more common medical conditions, such as kidney failure, liver disease and gastrointestinal disorders. Veterinarians usually focus on Addison's only after they eliminate other possible causes of the dog's symptoms. When assessing a dog with a history of lethargy, weakness, abdominal pain, vomiting, diarrhea, poor appetite and weight loss, the attending veterinarian will first perform a thorough physical examination. This includes looking in the mouth, palpating (feeling) the peripheral lymph nodes to see if they are enlarged, checking all over the body for lumps and bumps, assessing the condition of the coat and skin, and auscultating (listening to) the heart and lungs through a stethoscope. If Addison's is the dog's only medical problem, its physical examination results usually will be unremarkable.

Diagnostic Procedures
Based on the dog's symptoms and the results of the initial examination, most veterinarians will recommend conducting some basic blood work (a complete blood count and a serum biochemical profile) and a urinalysis. These routine tests, which involve collecting and evaluating blood and urine samples, are simple and relatively inexpensive. The results, together with the history and physical examination, may suggest a tentative diagnosis of Addison's – especially if they reveal low blood sodium levels (hyponatremia), low blood chloride levels (hypochloremia), high blood potassium levels (hyperkalemia) and high levels of circulating blood urea nitrogen (BUN), which is a waste product of metabolism. However, more advanced tests are required for Addison's to be definitively diagnosed.

The most conclusive test for Addison's Disease is an "ACTH stimulation test." "ACTH" is an abbreviation for "adrenocorticotropic hormone," a substance that is produced by the pituitary gland and, in normal dogs, stimulates the adrenal glands to produce other hormones, called "corticosteroids" or simply "steroids." Adrenal hormones are extremely important to the regulation of a number of bodily functions, including metabolism and fluid management. Dogs with Addison's have abnormally low levels of circulating adrenal steroids, which is why the disease medically is called "hypoadrenocorticism." The ACTH stimulation test involves administering ACTH, waiting a prescribed period of time and then reevaluating the dog's blood to see whether its adrenal glands have responded appropriately by producing more corticosteroids. In dogs with Addison's Disease, the ACTH injection will cause no or only a barely detectable increase in circulating steroids, because the adrenal glands are damaged and cannot respond normally to the ATCH stimulus.

This may seem simple. However, because the signs of Addison's Disease match those of so many more common disorders, ACTH stimulation tests usually are conducted only after other tests have ruled out more likely causes of the dog's condition. For example, vomiting and diarrhea - two common consequences of Adddison's – cause dehydration. Dehydrated dogs have abnormally low levels of circulating fluids, including blood, and abnormally high levels of circulating solids, including toxic waste products. These abnormalities can be detected on routine blood work. One of the easiest to identify is an increase in circulating blood urea nitrogen. Elevated BUN can be caused by Addison's. However, more often it is caused by kidney disease. Dogs with elevated BUN often are given intravenous fluids in an attempt to correct their dehydration and normalize circulating BUN levels. Dogs with kidney disease won't improve dramatically, because their kidneys are unable to filter out wastes regardless of their hydration level. On the other hand, BUN levels in dogs with Addison's Disease usually drop rapidly once hydration has been reestablished, since their kidneys are fine and can respond normally to increased fluid levels.

Attending veterinarians must systematically go through this process of assessing a dog's history, symptoms and physical state, performing appropriate tests and ruling-out the more common causes of its condition, in order to reach the right diagnosis. Although this can take some time, it usually is possible for Addison's to be diagnosed in time for effective treatment to take place.

Special Notes
If undiagnosed and untreated, Addison's can progress to what is called an "acute Addisonian crisis," which may rapidly become life-threatening.

Treatment Options

Treatment Goals
Addison's Disease, known as "hypoadrenocorticism" in medical circles, is a potentially fatal condition in dogs that cannot be cured but usually can be managed medically. The signs of Addison's are vague and include intermittent vomiting, diarrhea, weakness and abdominal pain. When an owner notices these symptoms, she should take her dog to a veterinarian and describe the onset of her pet's condition in as much detail as possible. Left untreated, Addison's will progressively worsen.

Normally, by the time a dog is diagnosed with Addison's Disease, at least 90% of its functional adrenal glands have been damaged or destroyed, making immediate medical treatment essential. Once the dog has been stabilized, its condition can be thoroughly assessed and proper management of its disease can begin. The goals of treating Addison's are to replace circulating fluid volume (reestablish hydration), correct electrolyte imbalances, relieve the dog's current discomfort and stabilize circulating levels of adrenal hormones by providing an immediate source of corticosteroids.

Treatment Options
How aggressively a dog will be treated for Addison's Disease depends in large part on how sick it is at the time it arrives at the hospital. Dogs suspected of being in an Addisonian crisis must be treated immediately on the assumption that they have hypoadrenocorticism, even before that diagnosis is confirmed. Waiting for the results of an ACTH stimulation test will put the dog's life at increased risk. Emergency treatment of a dog suffering from severe Addison's symptoms includes placing it on intravenous fluids (usually normal saline) and giving injections (rather than oral doses) of adrenal corticosteroid hormones. Dogs with Addison's Disease usually show marked improvement within 24 hours of in-patient treatment. An ACTH stimulation test should only be performed after the dog's medical crisis has stabilized. If Addison's is confirmed by the results of that test, the medical team will come up with an appropriate management protocol, after discussing the various options with the patient's owner.

Once the dog's circulating fluid, electrolyte and adrenal hormone levels are restored, and after it has recovered from any other adverse effects of the disease, it will be discharged from the clinic, and its owner finally will be able to take her pet home, where it undoubtedly will be more comfortable. In most cases, dogs with Addison's will need to be treated for the rest of their lives. Medical management involves lifelong supplementation with oral corticosteroids. The attending veterinarian will decide which drug(s) to administer based upon the nature and extent of the particular dog's disease. The veterinarian probably will recommend that the dog have urine and blood tests performed periodically, to monitor its circulating levels of sodium, chloride, potassium, electrolytes, blood urea nitrogen and adrenal corticosteroids. If abnormalities in those levels persist or recur, the dog may need more intensive therapy.

Prognosis
The prognosis for dogs with Addison's Disease is very good, as long as the owner is conscientious about administering daily medications and taking her companion to the veterinarian for regular blood and urine monitoring. Excellent communication between owners and their veterinarians is vital to the success of managing this uncommon but potentially life-threatening endocrine disorder.

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