Such is the case with Addison's disease, an adrenal gland disorder that can strike any breed of dog and any race of human, including former United States President John F. Kennedy. In cases of Addison's disease, the adrenal gland fails to produce enough steroid hormones, specifically two classes known as glucocorticoids and mineralocorticoids. The disease itself is named after British physician Dr. Thomas Addison, who first recognized and wrote about the problem in 1855.
The adrenal gland is located just in front of the kidney. The center of the gland is termed the medulla, while the outer area is the cortex. Both areas produce hormones, but Addison's disease involves hormones produced solely by the cortex. These are known as corticosteroids, and they in turn are the hormones used by both people and animals to physiologically cope with stress.
In canines, most affected animals are young female dogs that are between four and five years of age. The first symptoms are mild and usually include listlessness, vomiting, muscle weakness, joint and/or muscle pain, weight loss and diarrhea. Occasionally the dog may crave salty foods (due to an excess loss of sodium). Other diseases are often suspected first, meaning most animals aren't correctly diagnosed until they reach a state known as an "Addisonian crisis." This crisis results in the animal going into shock, since its digestive and circulatory systems do not have the hormones they need to help the body adapt to stress. When this occurs the dog's blood sugar may drop to dangerously low levels, while at the same time its potassium levels skyrocket, disrupting the heart rhythm. If not treated right away, dogs experiencing an Addisonian crisis do not survive.
In some cases Addison's disease can produce unusual symptoms, such as seizures or severe vomiting (caused by spasms in the esophagus), which are easily misdiagnosed. In fact, because of its ability to produce symptoms of many other disorders, Addison's disease is known in medical circles as "the Great Imitator." The disease does not appear to be passed genetically. However, female dogs with Addison's disease should not be bred, as their hormone imbalance makes pregnancy very dangerous to their health.
The chief cause of this disorder isn't yet known, although can occasionally appear as the result of damage from two medications that disrupt adrenal function (Ketoconazole and Lysodren). A definite diagnosis is made through blood tests and an exam known as the ACTH stimulation test. In this exam the animal is given a dose of ACTH, which is the pituitary hormone responsible for releasing corticosteroids when the body is under stress. In normal animals the level of the hormone cortisol will rise in response to ACTH. In dogs with Addison's disease, they have no corticosteroids, so their cortisol level cannot rise.
While hard to diagnose and occasionally fatal, the good news is that the symptoms of Addison's disease normally can be managed very well through daily corticosteroid hormone therapy, even when the underlying cause isn't known.