(Addison's Disease)
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is an uncommon but very serious endocrine disorder of dogs resulting in
a deficiency of adrenal gland hormones necessary for life. Left untreated
the disease is fatal.
CHA generally presents in one of two ways. In the chronic form of the
disease the dog may suffer recurrent episodes over many months with
signs including vomiting, lethargy and weakness, little or no appetite,
dehydration, weight loss and possibly diarrhea and may respond well to
symptomatic treatment for these signs.
CHA is often referred to as the "Great Pretender" since the signs of the
disease are non-specific and also seen in other more common diseases of
dogs such as kidney disease, inflammatory bowel disease, and intestinal
parasites. Quite often the condition is not diagnosed immediately or even
misdiagnosed until the dog becomes quite ill and diagnostic blood tests
are performed.
In the acute form of the disease the dog suffers an "Addisonian crisis"
with vomiting and weakness progressing to a complete collapse, slow
heartbeat and shock. This form of the disease is a life-threatening
emergency and requires immediate treatment.
Although any dog can be affected, certain breeds of dogs are much more
likely to develop CHA including Great Danes, Rottweillers, Standard
Poodles, Portuguese water dogs, and Wheaton terriers with an average
age of onset in young to middle-aged adults, two to six years of age. The
disease is also more common in females.
What are adrenal glands? The body has 2 adrenals, one located at each
end of the kidney. They produce several important hormones including
cortisol and aldosterone. Production of cortisol is under the control of
the pituitary gland at the base of the brain. The pituitary releases
"adrenocortical stimulating hormone" (ACTH) which in turn stimulates
the adrenal glands to release cortisol into the blood stream.
Cortisol, a glucocorticoid hormone, is involved in many processes
throughout the body. A deficiency of cortisol leads to many of the
clinical signs seen in CHA in addition to a decreased ability of the dog to
handle stressful situations.
Aldosterone, a mineralocorticoid hormone, regulates the sodium and
potassium balance of the body. A defeciency of this hormone results in
the inability of the body to retain sodium and excrete potassium. This
causes the blood level of sodium to drop and the potassium level to rise
to toxic levels resulting in a weak, slow heart rate. Low sodium and high
potassium is a classic sign of CHA seen on a chemistry panel.
The most common cause of CHA is thought to be an immune-mediated
destruction of the adrenal glands leading to a deficiency of both
glucocorticoids and mineralocorticoids. Other less common causes
include infection, cancer and long-term oral prednisone therapy which
causes the adrenal glands to atrophy. Rarely, the primary problem may
be in the pituitary gland causing a deficiency of ACTH which leads to a
deficient production of glucocorticoids only and is termed "atypical
hypoadrenocortisism". Sodium and potassium levels are normal in dogs
with atypical CHA.
How is CHA diagnosed? Blood testing is necessary to diagnose CHA.
Routine lab tests may demonstrate abnormal sodium and potassium
levels, low blood sugar, and anemia. However, some dogs with CHA
may have normal values on routine tests, especially early on in the
disease.
The test of choice for diagnosing CHA is the "ACTH Stimulation Test".
This test measures cortisol levels in the blood before and after the
administration of a dose of ACTH gel. Normal dogs will have a rise in
cortisol levels after the injection while dogs with CHA will not.
The treatment of CHA depends on what form of the disease the dog
presents with.
Dogs in an acute Addisonian crisis must be hospitalized and treated with
IV fluids and supplemented with a synthetic glucocorticoid such as
prednisone or dexamethasone, and a mineralocorticoid if the sodium and
potassium levels are abnormal. If treated early and aggressively enough
many dogs respond well to treatment and have a favorable prognosis.
Long term therapy for dogs with CHA includes daily supplementation
with oral prednisone plus or minus supplementation with either Florinef,
an oral mineralocorticoid, or Percorten-V, an injectable mineralocorticoid
to maintain normal electrolyte levels. Routine lab testing is necessary for
dogs with CHA to monitor sodium and potassium levels and adjust the
medications as necessary. Dosages may also have to be adjusted during
times of stress such as in illness or surgery.