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(HYPOADRENOCORTICISM)
THESE TERMS WILL BE USED INTERCHANGEABLY THROUGH THIS TEXT
ADRENAL HORMONES
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The Adrenal glands are
located just atop the kidney.
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The adrenal gland is so named because it is located just forward of the kidney ("renal" means kidney).
The center of the gland is
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The cortex
is shown
in yellow
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called the "medulla" and the outer area is called the "cortex." While both areas produce hormones, Addison's disease concerns the hormones produced by the cortex;
these hormones are called "corticosteroids."
Corticosteroids are the hormones that enable us to adapt physiologically to stress. The "Glucocorticoids"
(such as cortisol and related synthetics, prednisone and dexamethasone) act on the mechanics of sugar, fat, and protein metabolism. They gear the metabolism towards the preparation of burning (rather than storing)
fuels so as the be ready for a "fight or flight" situation.
The "Mineralocorticoids" (such as aldosterone and related synthetic fludrocortisone acetate) influence the electrolytes: sodium and potassium. As a general biological rule,
where there's sodium or salt, there's water. When the mineralocorticoids circulate as part of the "fight or flight" preparation, sodium is conserved in anticipation of blood
loss so that there will be extra fluid in the vascular compartment (spare blood). When sodium is conserved, potassium is lost as part of the biological balance. This whole
picture of fat mobilization, sodium conservation etc. which is part of the "fight or flight" preparation is far more complex than can be reviewed here but the bottom line is:
Corticosteroid hormones are needed to adapt to stressful situations and without these
hormones, even small stresses could lead to physiologic disaster.
HYPOADRENOCORTICISM (ADDISON'S DISEASE)
In animals with Addison's disease, there is a deficiency of the corticosteroid hormones.
It is unusual to discover the direct cause of this deficiency unless the patient is taking medications that disrupt adrenal balance (like Ketoconazole or Lysodren) but, fortunately, the disease can be managed with the administration of corticosteroid
hormones even if the cause of the deficiency is unknown.
CLINICAL SIGNS
Patients are usually young (age 4-5 years) female dogs. (This disease occurs in cats but
is very rare.) At first signs are very vague - listlessness, possibly some vomiting or diarrhea. Ultimately, the disease results in a phenomenon known as the "Addisonian crisis."
The animal collapses in shock due to its inability to adapt to the caloric and circulatory requirements in stress. Blood sugar may drop dangerously low. Potassium
levels soar and disrupt the heart rhythm because there is not enough conserved sodium to exchange for potassium. Heart rate slows, arrhythmias result. The patient may not survive this episode.
MAKING THE DIAGNOSIS
Veterinarians are usually presented with a young animal in shock. There is usually no
history of trauma or toxic exposure so general treatment for shock is initiated. This consists of rapid administration of fluids (usually lactated ringers solution which has
little potassium and a moderate amount of sodium) plus some glucocorticoids. By coincidence, this also happens to be similar to the specific treatment for Addison's
disease so that often the patient simply recovers without the veterinarian really knowing why.
The blood panel will come back showing elevations in the renal parameters (BUN and
Creatinine) and thus with the elevated potassium is suggestive of acute renal failure, a condition with an extremely poor prognosis. The veterinarian may become suspicious
of another diagnosis as the patient will respond well to fluid administration and most renal failure patients do not respond as well.
Addison’s disease may present in more unusual ways. Inability to maintain normal
sugar levels (ultimately manifesting as a seizure disorder) may be strongly suggestive of an insulin-secreting pancreatic tumor but before a major abdominal surgery is planned, it
is important to test for Addison’s disease.
Similarly unexpected, regurgitation of undigested food due to abnormal nerve function in the esophagus (a condition called “Megaesophagus”) can be caused ultimately by Addison’s disease.
Because of the numerous symptoms Addison’s disease can be present with, Addison’s
disease has earned the medical nickname “the Great Imitator.”
The only definitive test for Addison's disease is the ACTH stimulation test. The patient
receives a dose of ACTH, the pituitary hormone responsible for the release of corticosteroids in times of stress. A normal animal will show an elevation in cortisol in
response to ACTH while an Addisonian has no corticosteroids to respond with. This lack of response is diagnostic for Addison's disease; however, a false positive may be
obtained if corticosteroids have been used in the treatment of the crisis prior to the test. Only dexamethasone does not interfere with the assay for cortisol; if any other steroid
has been used, the test will not be valid for at least a couple of days.
TREATMENT AFTER THE CRISIS
The most important aspect of treatment for hypoadrenocorticism is the replacement of
the missing mineralocorticoids hormones. One way to do this is with oral Fludrocortisone (Florinef). Florinef is given usually twice a day at a dose determined by the patient's sodium and potassium blood tests. At first, these electrolytes are
monitored weekly. When levels seem stable, these blood tests are repeated 2-4 times per year. Often with time, it will be found that the dose of Florinef needed to control the
Addison's disease will increase. This is unfortunate as the medication is relatively expensive. Since Florinef has glucocorticoid activity as well as mineralocorticoid
activity, it is not necessary to use additional medications for treatment.
A nother way to treat this condition is with an injectable medication called
"DOCP”
(brand name “Percorten-V”). This treatment is given approximately
every 25 days. Electrolytes are measured prior to injections at first but testing can usually eventually be tapered to once or twice a year. There
is some feeling among experts that DOCP produces better regulation of electrolytes than does oral Florinef. Some dogs however, do require glucocorticoid supplementation (such as a low dose of prednisone).
Salting the patient's food is sometimes recommended to assist the patient with sodium balance.
SUCCESSFUL CASE STUDY: OTTER
 Otter was diagnosed with Addison’s disease and is doing well today thanks to the network of veterinarians servicing the America On-Line Pet Care Forum. Otter was nearing the
point of Addisonian crisis but the signs he was demonstrating were so vague that his regular vet could not pinpoint a diagnosis. Otter’s mom sought help on the Pet
Care Forum and was directed to an internal specialist in her area. Otter’s tests uncovered a clear case of Addison’s disease and proper treatment was initiated. Now that his
hormone deficiency is known, on-going hormone replacement keeps otter an active, happy boy.
Page last updated: 2/10/03
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