The adrenal gland is a gland located near the kidneys, which plays a very important role in the overall functioning of the body. When this gland becomes hyperactive, a disease called Cushing’s disease (see our information on this disease in the Archives) becomes apparent. Addison’s disease is the opposite, a deficiency in steroid production by the adrenals. Two types of steroids are produced by this gland: glucocorticoids and mineralocorticoids. Glucocorticoids (primarily cortisol and corticosterone) affect carbohydrate, protein, and lipid metabolism and regulate the immune system. Mineralocorticoids (the most potent being aldosterone) regulate electrolyte balance.
There are 2 types of Addison’s disease: primary and secondary insufficiency. Primary disease is the result of atrophy or destruction of all layers of the adrenal cortex, causing a deficiency of both gluco- and mineralocorticoids. Some of the factors causing primary disease are immune-mediated, fungal infection, cancer, hemorrhage, or therapy for Cushing’s disease. Secondary insufficiency results from insufficient pituitary secretion of ACTH (adrenocorticotropin, a hormone which regulates the adrenals), usually resulting in glucocorticoid deficiency only. Factors causing secondary disease are abrupt withdrawal of chronic or high-dose corticosteroid therapy, megestrol acetate (Ovaban) therapy in cats, and lesions (e.g., cancer) of the hypothalamus or pituitary gland.
Addison’s disease is mostly a disease of young- to middle-age dogs. The condition is rare in cats. The median age for dogs is 4-6 years, although it has been documented in dogs less than 1 year and up to 12 years of age. In general, about 70% of the affected dogs are female. Any breed may be affected, but the breeds that are most susceptible are standard poodles, bearded collies, Great Danes, Portuguese water dogs, West Highland white terriers, and rottweilers.
The typical patient with Addison’s disease shows signs of collapse and weakness and has a history of waxing and waning episodes of these signs. Affected dogs often have nonspecific gastrointestinal problems, such as anorexia, vomiting, or diarrhea. The waxing and waning signs of weakness and collapse are often associated with stressful events. If affected animals have electrolyte imbalances, they are quite ill and show the classical signs of collapse, slow heart rate (bradycardia), and shock.
The serum chemical profile may show changes such as low sodium, high potassium, and other nonspecific changes, whereas the complete blood count may not show the blood cell changes normally seen with stress. The definitive test for diagnosing Addison’s disease is the ACTH stimulation test. A baseline blood sample is drawn, a synthetic ACTH is injected to stimulate the adrenal gland, and another blood sample is drawn 1 hour later. Normal dogs show an increase level of serum cortisol during the test, whereas Addison’s patients show very little to no response.
If the dog has an acute episode of Addison’s disease and is very ill, treatment is directed to stabilizing the patient with intravenous fluids, immediate glucocorticoid therapy, and correction of electrolyte balances. Long-term therapy involves supplementation with mineralo- and/or glucocorticoids, depending on the type of Addison’s disease the patient has acquired. There are currently 3 medications available for treatment of this disease. Desoxycorticosterone pivalate (DOCP, Percorten-V), which is injected into the muscle every 3-4 weeks, has mineralocorticoid activity only. Some dogs may need to be supplemented with oral prednisone as well. Flurocortisone acetate (Florinef), a daily oral medication, has both mineralo- and glucocorticoid activity. Both treatment protocols are life long, and patients need to be monitored frequently. During times of stress (such as boarding or surgery) or illness, dogs may need higher doses of prednisone to keep them from going into an Addisonian crisis. In general, although untreated or irregularly treated Addison’s disease is frequently fatal, patients do very well on their medication once they get through their crisis