Hypoadrenocorticism, or Addison's disease, is a hormonal dysfunction due to a lack of production of steroids from the adrenal glands. The adrenal glands are paired organs that are found near both kidneys. They have numerous functions such as secreting the "fight or flight" hormone epinephrine, also known as adrenaline. They also secrete different types of hormones that regulate sodium and potassium levels, facilitate blood pressure regulation, and basic steroid homeostasis.
Addison's disease occurs when a specific type of steroid is not produced in sufficient quantities. Unlike many diseases that have typical clinical signs, Addison's clinical signs can vary tremendously. A veterinarian must have a suspicion of the disease as basic blood tests are often nonspecific. A detailed history is often the most important part of the diagnostic process. Many dogs with Addison's disease have a cyclical illness in that the patient may exhibit unexplained vomiting or diarrhea for a few days then improve only to begin the illness again within weeks. Weight loss is common as well. Some pets may exhibit mild abdominal pain that warrant x-rays to rule out other causes such as foreign bodies, obstructions, or masses.
As stated, most basic blood tests are within normal limits. However, a fair amount of patients will have a low sodium to potassium ratio. Since the adrenal gland maintains a specific relationship of sodium to potassium, an underactive gland will allow for sodium to decrease and potassium to increase. Even though the individual levels may still be a "normal" level, the ratio is bad. This often suggests a more specific blood test known as the ACTH stimulation test. The adrenal gland receives its commands from the pituitary gland located at the base of the brain. The pituitary secretes AdrenoCorticoTrophic Hormone or ACTH that tells the adrenal gland to respond. When we administer exogenous ACTH, we are trying to command the adrenal gland to respond. If the gland fails to do so, we then can diagnose hypoadrenocorticism, or Addison's disease.
Treatment involves replacing the missing hormone. This is accomplished by either injecting a hormone in the muscle once every 3-4 weeks, or by giving a daily tablet. Both forms are given for the life of the pet. Oral prednisone is often given in a very low dose as this hormone is produced in low levels with Addison's disease.