ADDISON’S DISEASE (HYPOADRENOCORTICISM)

ADRENAL HORMONES

The adrenal gland is located next to the kidneys. The center of the gland is called the "medulla" and the outer area is called the "cortex." While both areas produce hormones, Addison's disease involves the hormones produced by the cortex; called "corticosteroids."

In most cases, parts of the cortisone-producing adrenal glands waste away to such an extent they are only minimally functional. As a result, the adrenals don't produce enough of two types of cortisone crucial to your dog's ability to use energy-containing glucose and balance levels of critical minerals such as sodium and potassium. We aren't certain what causes the atrophy, but it is suspected the animal's immune system attacks its own adrenal glands. Occasionally, hypoadrenocorticism is due to a failure of brain-controlled mechanisms that stimulate the adrenal glands to secrete particular hormones.

Corticosteroids are the hormones that enable us to adapt physiologically to stress. The "glucocorticoids" (such as cortisol and related synthetics: prednisone and dexamethasone ) involve sugar, fat, and protein metabolism. They target the preparation of burning (rather than storing) fuels to react in "fight or flight" situations. In general, corticosteroid hormones are needed to adapt to stressful situations and without these hormones, even small stresses could lead to physiologic imbalances.

In animals with Addison's disease, there is a deficiency of the corticosteroid hormones. It is unusual to discover the cause of this deficiency unless the patient is taking medications that disrupt adrenal balance (like Ketoconazole or Lysodren). Fortunately, this disease can be managed with the administration of corticosteroid hormones even if the cause of the deficiency is unknown.

Patients are usually young (age 4-5 years) and are most often female dogs. (This disease occurs in cats but is very rare.) Predisposed breeds include: the Great Dane, the West Highland White Terrier, all sizes of Poodles, Portuguese Water Dogs, Rottweilers, and Soft-Coated Wheaton Terriers.

The first signs of Addison’s disease are vague and may include listlessness, weakness, appetite loss, weight loss, dehydration, vomiting or diarrhea. Some patients may experience increased thirst (polydipsia) and increased urine production (polyuria). Often patients have an inability to maintain normal sugar levels (ultimately manifesting as a seizure disorder). Others may experience regurgitation of undigested food due to abnormal nerve function in the esophagus (a condition called “Megaesophagus”).

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 during 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 and arrhythmias result. The end result may be death.