No discussion of Cushing’s disease would be complete without a look its antithesis, Addison’s disease, AKA “hypoadrenocortisism” or “adrenal insufficiency.”
Thomas Addison, a physician and one of the “Great Men” of Guy’s Hospital in London, first described the disease in 1855. Unlike Cushing’s disease, where the adrenal glands produce excessive amounts of cortisol, Addison’s disease patients are unable to produce adequate amounts of cortisol and related adrenal steroids. Bodies do not require large amounts of these substances, but what little the body needs is absolutely required or very, very bad things happen. Without a shot of cortisol in the morning, it’s tough to even get out of bed.
In a strange twist of history, Addison himself was something of the antithesis of Cushing. Where Cushing seems to have known everyone and done everything, Addison was a quiet and retiring man who kept a small practice focused largely on dermatology. It was recognition of the skin changes seen in humans that led Addison to discover the broad hormonal effects that result from inadequate adrenal gland function.
The adrenal gland is divided into two parts, the cortex and the medulla. The adrenal medulla is the central portion of the gland and produces important substances like epinephrine (AKA adrenalin), norepinephrine, and dopamine — none of which have any bearing on either Addison’s or Cushing’s disease.
The adrenal cortex, the outer layer of the gland, produces a variety of steroid hormones, including GLUCO-corticoids like cortisol, and MINERAL-corticoids, like aldosterone. The cortex also produces a variety of androgens, like testosterone. Steroid hormones have an extremely broad activity in regulating body functions. These hormones include everything from vitamin D to estrogen to DHEA to progesterone, and regulate everything from calcium uptake and bone density to gender characteristics and reproductive cycles.
So, Addison’s disease: What is it? The disease is sometimes referred to as “The Great Pretender,” causing anything from weakness and nondescript malaise to collapse and sudden death. Some patients present with loss of appetite, vomiting, or bloody diarrhea, others with sudden onset, severe shock-like signs in what is referred to as an “Addisonian Crisis.” The appearance of the disease depends on whether there is a deficiency in production of glucocorticoids (depression, poor appetite, low blood sugar) or mineral-corticoid (low sodium, decreased body fluid volume, low blood pressure, exercise intolerance, digestive problems), or both (any other sign you care to name including loss of body condition and hair loss). Some Addisonians have adrenal glands that work well enough most of the time, but run out of capacity during times of stress (“stress” is anything that’s unpleasant or really fun), resulting in intermittent problems. The result of these many alternatives is a disease that is extremely variable and may not be evident at all times, but is really a doozy when it shows up!
Famous Addison’s sufferers include President John F. Kennedy, author Jane Austin, mass murderer Osama bin Laden, and Bisquet (a cute little doggie whose last name is withheld for security purposes).
The causes of Addison’s disease are thought to be both genetic and/or autoimmune in people and dogs, but the immediate initiating causes are usually unknown in animals. Rare cases may result from administration of drugs used to treat Cushing’s disease. Addison’s disease is extremely rare in cats.
Diagnosis of Addison’s disease requires blood testing, the results of which run from completely deranged to perfectly normal. Adrenal response tests, where stimulating hormone is administered and the adrenal gland’s level of hormone secretion is measured, are the most reliable, but even these tests can be ambivalent. It takes an experienced veterinarian to recognize Addison’s disease because it so often looks like something else.
Once diagnosed, Addison’s disease is treated with low dose supplements of glucocorticoids, like prednisone, and mineralcorticoids, like fludrocortisone. The precise balance of gluco- and mineral-corticoids each patient requires is something that must be worked out by the veterinarian and the pet owner. All adrenal hormones can cause severe side effects when used over a lifetime, so careful monitoring is required to manage Addison’s disease. Most Addisonians live long and happy lives once their medications are “dialed in.”
This discussion of Addison’s and Cushing’s diseases has been a great way to talk about the complexities of adrenal gland function and two legendary doctors of the past. Readers will be glad I did not stick with my original version: “I Am Bob’s Adrenal Gland.”