(ADDISON'S DISEASE) IN DOGS
by Janice Madjanovich
Hypoadrenocorticism is a condition which results when the outer layer,
or cortex, of the adrenal glands fails in its secretion of the mineralocorticoid
and glucocorticoid hormones. It is often called Addison's disease after
the man who first described this syndrome in humans in 1855. It is not
a very common disease in dogs, but unfortunately Tollers have an increased
incidence of this condition. Middle-aged animals and particularly females
are most commonly affected.
The adrenal glands, which lie near the kidneys, have several important
functions. Different areas secrete different hormones, with several different
actions. The mineralocorticoids, of which the main one is called aldosterone,
are important in the regulation of electrolytes in the body. Their main
action is to conserve sodium, chiefly by promoting reabsorption by the
kidneys. Water follows the sodium, so they indirectly affect the water
balance of the body. They are also responsible for excreting potassium.
The main glucocorticoid hormone is cortisol. Cortisol is essential in
an animal's response to physical and mental stress. Cortisol levels rise
when an animal is stressed. This hormone has many metabolic effects.
Primary adrenal insufficiency results from destruction of the adrenal
cortex. The most common cause of this is immune-mediated destruction of
the adrenal gland. Like other immune-mediated diseases, Addison's is thought
to have a familial pattern. It is not common in vizslas, but some lines
of standard poodles have been devastated by this disease. Other rarer
conditions (e.g. tumor) resulting in destruction of the adrenal gland
can also cause primary hypoadrenocorticism.
Hypoadrenocorticism can also be induced. If an animal is being given
corticosteroid drugs such as prednisone, its body stops producing its
own corticosteroids. If the drug administration is abruptly stopped, the
dog can't start making it again fast enough, and can go into an Addisonian
crisis. For this reason, dosages of corticosteroids must always be tapered
Lack of cortisol affects most tissues in the body. Tolerance to stress
is reduced. The animal may develop vomiting, diarrhea, loss of appetite,
and weight loss. The mental state may be abnormal: lethargic or depressed.
Glucose production is decreased.
Without aldosterone, a dog cannot conserve sodium and is unable to get
rid of potassium. Water and chloride are lost along with the sodium. The
animal may become dehydrated or weak. The increased potassium results
in a slow heart rate and muscle weakness.
Not surprisingly, the signs of Addison's disease tend to be a combination
of the results of both lack of cortisol and lack of aldosterone (although
occasionally only cortisol is deficient). In a study of 100 dogs with
hypoadrenocorticism, the following were the most common findings:
Loss of appetite 77%
Weight loss 23%
Increased urination 15%
Waxing/waning signs 10%
Abdominal pain 9%
Owners may only notice progressive, intermittent, vague problems, or
the dog may go into acute adrenal crisis and have severely slowed heart
rate, shock, dehydration, and weak pulses.
Since the signs of Addison's disease are not very specific, the diagnosis
must be confirmed with laboratory tests. Blood tests will usually reveal
low levels of sodium and high levels of potassium. The definitive test
is the ACTH stimulation test. Administration of ACTH stimulates the release
of cortisol in normal animals. If the cortisol level is low before the
is given ACTH, and stays low afterwards, this confirms that the dog is
Fortunately, most dogs with hypoadrenocorticism respond very well to
treatment with mineralocorticoid drugs. If they are severely ill, they
may need therapy such as intravenous fluids to stabilize their condition.
The blood sodium and potassium levels are monitored and the drug dosage
adjusted accordingly over 3 to 4 weeks, and then checked every 3-4 months.
The two most commonly used are fludrocortisone acetate ("Florinef,")
given orally daily, and desoxycorticosterone pivalate ("DOCP"),
a long-acting injectable given once every 25 days. While most dogs are
well controlled on Florinef, the majority have more normal electrolyte
balances and feel better when treated with DOCP. As well as mineralocorticoid
replacement, about 50% of dogs will also need glucocorticoids, particularly
in times of
stress. Usually prednisone is used, and the dose can be increased when
the dog is stressed.