Definition
Addison’s disease, also known as hypoadrenocorticisim, is a condition that affects one or both of a dog’s adrenal glands, which are located just above the kidneys. Anything that damages the adrenal glands can trigger Addison’s disease. Dogs with this disorder don’t make enough adrenal hormones, which are critical to almost every aspect of bodily function. This causes circulating levels of glucose, potassium, sodium and chloride to become imbalanced, leading to dehydration and severe problems with vital organs, especially the heart. Affected dogs feel lousy, especially when they are under stress. They experience belly pain, nausea, vomiting, diarrhea, weakness, depression and other unpleasant symptoms, which typically come in waves. They may collapse for no apparent reason. Owners should be tuned in to the signs of Addison’s disease, so that they can get effective treatment for their beloved companions as soon as possible.
Causes of Addison’s Disease
Veterinarians are not always able to determine why their patients develop Addison’s Disease. In the most general sense, Addison’s is caused by some severe insult to the outer layer (cortex) of one or both of the adrenal glands, which causes all or part of the cortex to waste away. This, in turn, reduces or eliminates production and secretion of the corticosteroid hormones that are critical to normal body function. One of the most recognized causes of Addison’s Disease in dogs is autoimmune-mediated destruction of the adrenal cortices. Autoimmune disorders occur when a dog’s complex, finely-tuned immune system malfunctions and starts to attack the dog’s own tissues – in this case, the adrenal glands. Immune-mediated Addison’s in dogs usually happens for no known reason; this is called “idiopathic” Addison’s.
Other things that can damage the adrenal cortex include:
- Ingestions of toxic drugs or chemicals
- Physical trauma
- Adrenal tumors/cancer
- Genetic predisposition
- Infection
- Granulomatous disease (histoplasmosis, tuberculosis and blastomycosis can lead to formulation of tumor-like masses of granulation tissue in the adrenal glands)
- Administration of the drug mitotane to treat Cushing’s Disease
- Adrenocortical amyloidosis
- Long-term administration of steroid hormones. Over time, steroid therapy suppresses the body’s normal production of corticosteroids, because they are coming in sufficient amounts from the outside. This can cause the adrenal glands to atrophy from disuse and become non-functional.
When there are not enough corticosteroid hormones circulating through a dog’s bloodstream, the levels of glucose, potassium, sodium and chloride can quickly become imbalanced. This, in turn, can cause severe dehydration, depletion of the normal volume of circulating blood and significant problems with the animal’s heart and other vital organs. This is what is known as an “Addisonian crisis.” A dog in an Addisonian crisis must be hospitalized immediately and treated aggressively to have a realistic chance of pulling through.
An acute Addisonian crisis can happen when corticosteroid drugs that have been administered to a dog for a long time are abruptly withdrawn. While the dog is receiving the steroids, its adrenal glands go into a sort of resting state. When the external steroids are stopped, the dog can develop an extremely serious shortage of circulating adrenal hormones, which can cause shock and cardiovascular collapse. If the adrenal glands have atrophied or been “resting” for too long, the dog may not recover.
Ultimately, anything that damages the adrenal glands’ ability to produce a normal amount of corticosteroids can contribute to Addison’s Disease in dogs.
Prevention of Addison’s Disease
There is no fool-proof way to prevent canine Addison’s Disease, since the exact causes of this ailment are unclear. Avoiding abdominal trauma and weaning dogs off long-term steroid therapy can prevent some types of hypoadrenocorticism.
Special Notes
If diagnosis and treatment are delayed for too long, Addison’s Disease can be fatal.
Initial Evaluation
Addison’s Disease is uncommon in dogs and can be difficult to diagnose because it mimics many common medical conditions such as kidney failure, liver disease and gastrointestinal ailments. Veterinarians often focus on Addison’s only after eliminating other causes of the dog’s symptoms. Dogs with Addison’s usually present with a history of lethargy, weakness, abdominal pain, vomiting, diarrhea, poor appetite and weight loss. The veterinarian will perform a thorough physical examination, looking in the mouth, palpating the peripheral lymph nodes to see if they are enlarged, checking for obvious lumps and bumps, assessing the condition of the coat and skin, and listening to the heart and lungs. If Addison’s is the dog’s primary medical problem, its physical examination usually will be unremarkable.
Diagnostic Procedures
Based on the dog’s symptoms and the results of the initial evaluation, most veterinarians will recommend routine blood work including complete blood count and serum biochemical profile, as well as a urinalysis. The results 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). However, more advanced tests are required for Addison’s to be diagnosed definitively.
The most conclusive test for Addison’s is an adrenocorticotropic hormone (ACTH) stimulation test. In normal dogs, ACTH is produced by the pituitary gland and stimulates the adrenal glands to produce corticosteroids when the body needs them. The ACTH stimulation test involves measuring a dog’s blood steroid levels, and then administering ACTH. After a prescribed period of time, the levels of circulating corticosteroids will be reassessed. Dogs with Addison’s will have a barely detectable increase in blood steroid levels – or none at all, because their damaged adrenal glands can’t respond to the ATCH stimulus.
This sounds simple, however; because the signs of Addison’s Disease are so non-specific, the ACTH stimulation test usually is used only after other tests rule out more likely causes of the dog’s condition. For example, vomiting and diarrhea - two consequences of Addison’s – cause dehydration. Dehydrated dogs have a low blood volume with abnormally high levels of circulating solids. Basically, dehydration means that the fluid part of blood is too low, which makes the other components of blood too concentrated. These abnormalities can be detected on routine blood work. One of the easiest to identify is an increase in circulating blood urea nitrogen (BUN). Elevated BUN can be caused by Addison’s, because many Addisonian dogs are dehydrated. However, high BUN is much more commonly caused by kidney disease. Dogs with elevated BUN can be given intravenous fluids in an attempt to correct their dehydration and normalize their BUN levels. Dogs with kidney disease won’t improve dramatically after fluid therapy, because their kidneys can’t filter wastes from the blood regardless of their hydration level. However, BUN levels in dogs with Addison’s usually drop rapidly once they are rehydrated, because their kidneys respond normally to increased fluid levels. Most veterinarians diagnosing a dehydrated dog will therefore give them fluids before doing an ACTH stimulation test.
Special Notes
Although diagnosing Addison’s Disease can take some time, it usually is possible for veterinarians to diagnose it accurately in time for effective treatment to take place. By the time a dog is diagnosed, emergency medical treatment normally is necessary.
Effects of Addison’s Disease – From The Dog’s Point of View
Addison’s Disease affects different dogs in different ways and can vary widely among affected animals. The symptoms of Addison’s typically wax and wane, which means that they come and go over time. They can swing from mild to extremely severe for no apparent reason. Dogs with this disease tend to feel lousy in waves, especially when they are under stress such as during show, travel or boarding situations. They may experience belly pain, nausea, vomiting, diarrhea, weakness, depression and other unpleasant symptoms of systemic illness.
Symptoms of Addison’s Disease – What The Owner Sees
Most experts agree that up to 90% of the adrenal cortex must be damaged or destroyed before a dog will show significant signs of Addison's Disease. While the symptoms of Addison’s in dogs are notoriously non-specific and can be caused by a number of different disorders, most attentive owners eventually spot the symptoms in their companions, even though they may not know why they are happening.
Outward signs of Addison’s may include one or more of the following:
- Weakness
- Lethargy; listnessness
- Lack of appetite
- Vomiting
- Regurgitation
- Slow pulse (bracycardia)
- Diarrhea (+/- blood in stool)
- Weight loss (often severe)
- Abdominal pain
- Poor skin and coat condition (dry; patchy; flaky; dull)
- Increased thirst and water intake (polydypsia)
- Increased volume of urine output (polyuria)
- Shaking, trembling and shivering (neurological signs; with severe disease)
- Shock
- Seizures
- Collapse
- Coma
- Death
Addison’s may be suspected when a dog deviates from its normal activities or routine for no apparent reason. For instance, if a dog is reluctant to jump on a couch or bed that it usually leaps onto happily, the owner should pay attention, because pain and muscle weakness from Addison’s could be contributing to the dog’s discomfort. While all of the above signs can be associated with other disorders, the symptoms of Addison’s usually become more severe and more frequent 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.
Dogs At Increased Risk
Addison’s Disease is most commonly seen in young to middle-aged female dogs between 4 and 6 years of age. However, dogs of any age or gender can be affected. It is not entirely clear whether there are definitive breed predispositions for developing Addison’s Disease. 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/or Portuguese Water Dogs are at increased risk. Because of this, a genetic component is suspected.
Treatment Goals
Addison’s Disease is a potentially fatal condition in dogs that usually cannot be cured but typically can be well-managed medically. Normally, by the time a dog is diagnosed with Addison’s, about 90% of its functional adrenal tissue has been damaged or destroyed, making immediate treatment essential. The goals of treating a dog in an acute Addisonian crisis are to correct life-threatening low blood volume, low blood pressure, elevated circulating potassium and low blood glucose. Once the dog has been stabilized, therapeutic goals are to increase circulating fluid volume (reestablish hydration), correct electrolyte imbalances, relieve the dog’s discomfort and normalize blood levels of adrenal corticosteroid hormones.
Treatment Options
How aggressively a dog will be treated for Addison’s depends upon how sick it is when it arrives at the hospital. Dogs suspected of being in an Addisonian crisis will be treated immediately on the assumption that they have hypoadrenocorticism. Waiting for a definitive diagnosis of Addison’s under those conditions can put the dog’s life at great risk. Emergency inpatient treatment for a dog with severe symptoms probably will include placing it on intravenous fluids (usually normal saline) and giving injections rather than oral doses of corticosteroid hormones. Dogs with Addison’s Disease usually show marked improvement within 24 hours of this treatment. An ACTH stimulation test usually will 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 treatment and management protocol, and will discuss the various options with the patient’s owner. Once the dog’s fluid, electrolyte and adrenal hormone levels are normalized, and after it has recovered from any other adverse effects of the disease, it will be discharged from the clinic.
Most dogs with Addison’s Disease will need to be treated for the rest of their lives. Medical management involves lifelong supplementation with oral corticosteroids. The attending veterinarian will recommend which drug(s) to administer based upon the nature and extent of the particular dog’s disease. Urine and blood tests will probably be performed periodically to monitor the dog’s circulating levels of sodium, chloride, potassium, glucose, blood urea nitrogen and adrenal corticosteroid hormones. If abnormalities in those levels recur and persist, the dog may need more intensive advanced therapy.
Prognosis
Unfortunately, most cases of Addison’s Disease can’t be completely cured. Fortunately, however, the prognosis for dogs with Addison’s is usually very good, as long as the condition is caught and treated fairly early in its course. The owner must be conscientious about administering daily medications and taking her companion to the veterinarian for regular blood and urine monitoring.
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