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Overview of Canine Hypoadrenocorticism (Addison’s Disease)
Hypoadrenocorticism, also called Addison’s disease, is an endocrine disorder that results from a deficient production of adrenal gland hormones that can occur in dogs. There are two adrenal glands in the abdomen that lie just in front of the kidneys.
The most common cause of Addison’s disease in the dog is destruction of the adrenal gland tissue by the animal’s immune system. Infrequently, certain infections, medications, cancer or diseases of the pituitary gland may also cause Addison’s disease.
Addison’s disease may also be caused by the abrupt discontinuation of steroid medication. Dogs that have been on long-term steroids should be slowly weaned off such drugs. Abruptly stopping the medication can result in an Addisonian crisis.
Addison’s disease is an uncommon disorder in dogs and is extremely rare in cats. It is thought to be familial and inherited in Leonbergers, standard poodles, and Nova Scotia duck tolling retrievers. Certain other breeds may also be predisposed, such as the Airedale, bearded collie, German shepherd dog, German shorthair pointer, Great Dane, St. Bernard, English springer spaniel, West Highland white terrier, wheaten terrier, and Portuguese water dog.
Hypoadrenocorticism most often affects young to middle-aged dogs. About 70 percent of affected dogs are female. Neutered male dogs are more likely to develop hypoadrenocorticism than intact male dogs.
In hypoadrenocorticism there is usually a deficiency of two different groups of hormones, the glucocorticoids and the mineralocorticoids. The primary glucocorticoid hormone is cortisol, and it is responsible for combating stress, helping to maintain blood sugar. The major mineralocorticoid is aldosterone. Aldosterone regulates the water, sodium, potassium, and chloride concentrations in the body. Most naturally occurring forms of Addison’s disease affects both hormones. Addison’s disease secondary to the abrupt withdrawal of steroid medications affects only the level of circulating cortisol.
What to Watch For
The clinical signs seen with Addison’s disease are somewhat variable. They may be mild and very vague initially. With an acute crisis, the signs are more pronounced and profound. Clinical signs include:
- Lethargy, weakness
- Poor appetite
- Weight loss
- Excessive thirst and water intake (polydipsia)
- Low body temperature, shaking, collapse, low heart rate
Diagnosis of Hypoadrenocorticism (Addison’s Disease) in Dogs
Because hypoadrenocorticism can mimic many other diseases, diagnostic tests are needed to confirm the presence of Addison’s disease, and to exclude other diseases that cause similar signs. These tests may include:
- Complete medical history and physical examination
- A complete blood count (CBC), blood biochemistry profile and urinalysis
- An ACTH stimulation test (the diagnostic test of choice)
- Chest and abdominal radiographs (X-rays) and possible abdominal ultrasound, depending on the clinical symptoms
Treatment of Hypoadrenocorticism (Addison’s Disease) in Dogs
Treatment depends on whether the onset of illness is acute with severe symptoms, or whether more mild, chronic signs are present. For acute disease (an Addisonian crisis) treatment may include:
- Intravenous fluid therapy
- Electrolyte and acid-base monitoring
- Corticosteroid and mineralocorticoid replacement therapy
Treatment for chronic disease may include:
- Corticosteroid and mineralocorticoid replacement therapy
- Daily salt supplementation
At home, administer any prescribed medication precisely as directed by your veterinarian. Observe the dog’s activity level, appetite and water intake. Also, report any occurrence of vomiting, diarrhea, weakness, and change in appetite to your veterinarian immediately. Regularly scheduled veterinary visits are needed to monitor the disease and response to treatment. Such exams often involve various tests to monitor the levels of sodium and potassium in the blood.
Some dogs have different medication needs during times of stress such as travel, surgery, or hospitalization. Be sure to discuss this with your veterinarian if you anticipate times of stress in the future.
There is no preventative measure for the naturally occurring forms of this disease. If your dog is receiving steroid medication, do not stop the medication abruptly. By doing so, an Addisonian crisis can occur. This is the only form of Addison’s disease that is preventable.
In-depth Information on Hypoadrenocorticism (Addison’s Disease) in Dogs
Hypoadrenocorticism is a relatively uncommon disease, but it is highly treatable. Nevertheless, without proper veterinary care, the condition can be fatal. Because the history, clinical signs, and presentation of dogs with hypoadrenocorticism are so variable, there are other illnesses that must initially be considered when establishing a definitive diagnosis. These illnesses may include:
- Gastrointestinal (GI) foreign bodies that cause vomiting, diarrhea, and weakness
- Infections of the gastrointestinal tract with bacteria (Salmonella, Campylobactor, Clostridia), viruses (parvovirus, coronavirus), fungi (histoplasmosis), or parasites (whipworms)
- Neoplasia (cancer) of the gastrointestinal tract, such as lymphosarcoma and adenocarcinoma
- Inflammatory bowel disease (IBD), a syndrome of chronic intestinal inflammation
- Kidney diseases, such as acute kidney failure and pyelonephritis (infection of the kidney)
- Pancreatitis, an inflammation of the pancreas that causes severe vomiting and diarrhea
- Urinary blockage resulting in hyperkalemia (high blood potassium) and azotemia (abnormal kidney function test)
- Diseases causing hypercalcemia (high blood calcium levels), such as cancer and parathyroid gland diseases
Veterinary care includes diagnostic tests to identify the presence of Addison’s disease, determine any underlying causes, and help guide subsequent treatment recommendations.
Certain diagnostic tests are needed to diagnose hypoadrenocorticism and exclude other diseases that may cause similar symptoms:
- A complete history and thorough physical examination are initially performed. Special attention is paid to abdominal palpation (eliminating foreign bodies or abdominal masses) and thoracic auscultation (listening carefully for an irregular or slow heart rhythm).
- A complete blood count may show a mild anemia (low red blood cell count), or mild elevation in eosinophils and lymphocytes (certain types of white blood cells).
- A biochemical profile may initially be normal, or may show elevations in kidney tests, serum potassium, serum phosphorus, and serum calcium. Usually sodium and chloride levels in the blood are low. Occasionally blood sugar is also low.
- A urinalysis may show very dilute (watery) urine.
- A fecal test is performed to rule out the presence of intestinal parasites.
- Chest X-rays may show a small heart and small blood vessels leading to the heart if the animal is collapsed, dehydrated and in shock.
- Abdominal X-rays help exclude a gastrointestinal foreign body or mass as the cause and are often normal.
- An abdominal ultrasound may be needed to rule out kidney disease, other urinary tract problems, and to assess the size of the adrenal glands.
- An electrocardiogram (EKG) may be recommended, and may show an abnormally slow heart rhythm, which arises with severe hyperkalemia.
- Measuring blood pressure may be considered in weak or collapsed animals.
- An ACTH stimulation test is a blood test that measures adrenal gland function. This test is the best means of confirming the diagnosis. It is a timed test that your veterinarian can usually perform.
- Your veterinarian may recommend additional tests to exclude or diagnose other conditions. Such tests are selected on a case-by-case basis. They include the measurement of certain other circulating hormones, such as the pituitary hormones, thyroid hormones, and parathyroid hormone.
Treatment of hypoadrenocorticism must be individualized for each patient. Treatment may necessitate immediate hospitalization in those cases of extreme weakness, collapse, or shock. However, in other cases, medical management can be instituted as an outpatient. Treatments may include:
- Very aggressive therapy is indicated for those cases in shock, those with severe electrolyte abnormalities, abnormal kidney function tests, high calcium levels, low blood sugar, and abnormal heart rhythms.
- Intravenous fluid therapy is very important, and often involves administration of a normal saline solution to bring sodium levels back up to normal, and to lower calcium and potassium levels.
- Other therapy may also be needed to lower blood potassium.
- Glucocorticoids (dexamethasone or prednisone) are indicated during treatment of an acute crisis state. Depending on the individual case, they may or may not be recommended for long-term therapy.
- Mineralocorticoids are started in all cases of hypoadrenocorticism. They are available in either injectable (DOCP) or oral (Florinef®) forms, and are usually required for the lifetime of the dog.DOCP (desoxycorticosterone pivalate) Percorten-V® is an injectable medication that is administered by your veterinarian every 3 – 4 weeks, with the exact interval being established by frequent blood test monitoring.
- Florinef® (fludrocortisone acetate) is an oral medication administered once or twice daily. It is the more commonly used mineralocorticoid, although it requires excellent owner compliance and is quite costly.
Follow-up Care for Dogs with Addison’s Disease
Optimal treatment requires a combination of home and professional veterinary care. It is very important that all medication be administered exactly as prescribed by your veterinarian. It is also important that you observe your dog very closely and report any abnormalities to your veterinarian promptly. Although certain symptoms such as vomiting or diarrhea may be seen on occasion in a normal, healthy dog, it is best to report them when the dog has a history of hypoadrenocorticism.
Avoid and/or prepare for any situation that might cause physical or emotional stress to your animal. This includes strenuous exercise, marked changes in your dog’s routine or environment, and surgery. If such situations cannot be avoided, your veterinarian may recommend adjustments in your dog’s treatment regime to help him cope with any upcoming stress.
It is important to keep regularly scheduled veterinary visits for examination and blood electrolyte monitoring. Initially these visits occur every 2 to 3 weeks, with adjustments made to medications as indicated by the test results. Gradually the recheck visits are decreased to every 3 to 4 months, and eventually to every 6 months in the stable patient. If your dog is on injectable DOCP, veterinary visits are necessary every 3 to 4 weeks so that the injection can be administered.
Most dogs with hypoadrenocorticism have an excellent prognosis after proper stabilization and treatment.