Addison’s Disease in Dogs and Cats

Hypoadrenocorticism, also called Addison’s disease, is an uncommon, but serious, disease that affects the adrenal glands. This illness is rare in dogs and extremely uncommon in cats.

Addison’s disease can cause acute medical crises, but, fortunately, is extremely treatable. With proper diagnosis and treatment, pets can live a normal life.

Who Is Affected by Addison’s Disease?

Addison’s disease is most commonly diagnosed in younger female dogs, though it is also recognized in males. There are some breeds that appear to be predisposed to hypoadrenocorticism.

These breeds are:

• Standard Poodles
• West Highland Terriers
• Labrador Retrievers
• Great Danes
• Soft Coated Wheaten Terriers
• Portuguese Water Dogs

What Is Addison’s Disease?

The adrenal glands are a part of the endocrine system. The adrenal gland is broken down into three outer regions and a medulla, with different hormones being produced based on the region. The outermost layer is the zona glomerulosa, which produces mineralocorticoids like aldosterone. The middle layer is zona fasciculata, which produces glucocorticoids like cortisol. The inner layer is the zona reticularis, where sex hormones, estrogen, and testosterone are produced. The medulla, the innermost area of the adrenal gland is where catecholamines such as epinephrine and norepinephrine are made.

There are two types of steroid hormones: glucocorticoids and mineralocorticoids. The primary glucocorticoid is called cortisol and the primary mineralocorticoid is called aldosterone. In common cases of hypoadrenocorticism, these steroid hormones are deficient. In atypical cases of Addison’s disease, only glucocorticoid secretion is affected.

An insufficiency of cortisol and aldosterone can have a marked impact on the body. Cortisol is an important hormone that plays a role in most major tissue groups. It stimulates appetite, maintains the blood glucose, prompts the breakdown of fats and proteins, stimulates red blood cell formation, protects against shock, and balances the effects of stress on the body.
Aldosterone works to control the water and salt balance in the body. This also helps maintain blood pressure. Any disruption of this process can cause changes in the levels of sodium and potassium in the blood serum, affecting the kidneys, heart, and circulatory system.

Causes of Addison’s Disease

Veterinarians are not exactly sure what causes hypoadrenocorticism. It is considered an idiopathic disease, which is any disease that occurs for no apparent reason. Many veterinarians believe that it may be immune mediated, meaning that it is caused by an abnormal response of the body’s immune system.

Addison’s disease can also be brought on by medication for other illnesses. An overdose of medication used to treat Cushing’s disease (hyperadrenocorticism), a disease in which there is an excess of adrenal hormones, can cause an Addisonian crisis in response. Abruptly stopping a course of steroids, such as prednisone, can also cause a crisis. Pets should always be weaned off of steroid medications slowly. It is important to follow your veterinarian’s directions when giving your pet steroids.

Signs of Addison’s Disease

The wide range of symptoms related to hypoadrenocorticism make it difficult to recognize progressive disease. Most signs are very similar to those of many other diseases, which has earned Addison’s disease the nickname “The Great Pretender”. These symptoms may come and go, making it even more difficult to recognize chronic illness.

Symptoms include:

• Vomiting
• Diarrhea
• Lethargy/depression
• Anorexia (not eating)
• Drinking excessively (polydipsia)
• Urinating excessively (polyuria)
• Weight loss

These signs may not be recognized as problems until the animal goes into an Addisonian crisis, which is an acute medical emergency. During a crisis, a pet experiences life-threatening symptoms, including collapse and dehydration-related shock. These patients may also have pale mucous membranes and profound weakness. Without immediate medical treatment, their condition may be fatal.

Diagnosis

In order to properly assess a patient that is suspected to have Addison’s disease, a veterinarian will need a full medical history, physical exam, and blood testing.

Typical blood tests for this condition include:

• CBC (complete blood count), since anemia is a common symptom in Addisonian pets.
• Biochemistry panel, since elevations of kidney values can be seen during an Addisonian crisis.
• Urinalysis.
• Electrolyte panel. Electrolyte abnormalities commonly seen in hypoadrenocorticism include low sodium and high potassium. The change in potassium can have a profound effect on a patient’s heart, causing a slower than normal heart rate (bradycardia).
  • An elevated potassium and low sodium are classic changes expected with a typical Addisonian crisis. Pets that have atypical Addisonian disease do not have electrolyte changes.

The only definitive test to diagnose suspected hypoadrenocorticism is an adrenocorticotropic hormone (ACTH) stimulation test. This is a simple blood test that measures how well the adrenal glands respond to ACTH. ACTH is produced in the pituitary gland and stimulates cortisol release from the adrenal glands.

An animal will have a blood sample drawn before being given an injection of synthetic ACTH (Cortrosyn). This is called a pre-sample. They are then injected with a dose of Cortrosyn based on their weight. A second sample will be drawn one hour after the injection of the synthetic hormone. These samples will be sent to a lab for analysis. Diagnosis of hypoadrenocorticism is made if the patient’s adrenal glands do not respond with an elevated cortisol after the ACTH stimulation test.

Treatment

A patient in crisis will require stabilization before any testing for suspected hypoadrenocorticism can be done. These patients will need to be admitted to the hospital for intense treatment during their Addisonian crisis. Treatment will be symptomatic, focusing on intravenous fluids for dehydration, correcting any acid-base and electrolyte abnormalities, and glucocorticoid replacement. Electrolyte abnormalities may correct themselves as the patient is rehydrated. Life-threatening abnormalities, such as high potassium manifesting as bradycardia (slow heart rate), require treatment with medication.

Elevated potassium is treated with:

• Insulin. Insulin is a fast-acting treatment that is given to expedite the uptake of glucose into cells, bringing potassium with it. Insulin lowers blood glucose levels, so it is important to supplement these patients with glucose until the effects of the insulin wear off.
• Albuterol. Albuterol is a beta-adrenergic agonist which binds to receptors on cardiac tissue. It increases heart rate and contractility. In addition, it helps to shift potassium into the intercellular space. It is given in inhaler form through a mask and is quick acting.
• Calcium Gluconate. For protection of the heart, calcium gluconate is given intravenously. It has no direct effect on the blood serum levels of potassium, it is only cardioprotective, so it is most useful when given with other medications. These patients will need to be attached to electrocardiograms to monitor the electrical activity of their heart and closely monitored during treatment. They may require long periods of hospitalization.

Long-term treatment of hyperadrenocorticism includes glucocorticoid and mineralocorticoid replacement therapy. Glucocorticoid supplementation is achieved with an oral steroid, such as prednisone or prednisolone. Mineralocorticoid supplementation can be adminstered with either a monthly injectable medication at your veterinarian’s office (desoxycorticosterone pivalate) or a daily oral medication at home (fludrocortisone acetate, branded as Florinef). Florinef is a medication that provides both glucocorticoid and mineralocorticoid supplementation.

Atypical Addison’s is treated in much the same way, however, only glucocorticoid supplementation is needed. This is accomplished by using an oral steroid. The goal is to use the lowest effective dose of steroid to control the symptoms. This helps to minimize side effects from the steroid medication, such as excessive drinking and urinating. Since the pet will need this medication for the rest of their life, giving the smallest dose necessary will also decrease the likelihood that the pet will exhibit signs of hyperadrenocorticism secondary to the medication dose.

Follow-up

Patients will need to be monitored closely. For the first 2 – 3 weeks of recovery after diagnosis, recheck appointments, including electrolyte testing, will be required every 5 – 7 days to ensure medications are having the desired effect. After that, patients will need to have their electrolytes checked every 3 – 4 months for the first year. After the first year, it is recommended that patients have their electrolytes checked at least once a year, assuming there are no concerns. In times of stress, owners may find that medications do not appear to be working and testing will need to be done to see if they should be adjusted.

Prognosis

Prognosis for animals with hypoadrenocorticism is excellent if they are well-controlled. Unfortunately, there is no cure for Addison’s disease. The pet will need replacement hormones for the rest of their life. Animals will also need regular follow-up exams and blood work. This is a sizable commitment for a pet owner, but it is rewarding. With proper treatment and a lifelong commitment to your animal’s health, a normal life span can be expected.