Hypoadrenocorticism, more commonly known as Addison’s Disease, is an endocrine disease in which the adrenal glands do not produce enough glucocorticoids and/or mineralocorticoids. It can be due to either an immune system-mediated destruction of the adrenal gland cortices or due to Adrenocorticotropic hormone (ACTH) deficiency in the pituitary.
The pituitary gland is what sends a signal (ACTH) to the adrenal glands to tell them to make glucocorticoids and mineralocorticoids. The latter two compounds play many roles throughout the body, including glucose regulation, stress response, sodium regulation and potassium regulation. These roles may seem obscure to someone not familiar with medicine, but in a nutshell, all you need to know is that they are really important for a body to function properly.
Perhaps one of the most critical effects of Addison’s disease is the disruption of sodium and potassium balance in the body. An drastic decrease in sodium can result in extreme water depletion. This can cause many problems in the body, mainly depression, hypotension, and azotemia. This disease also causes potassium to not be excreted and instead increases in the body. This increase in potassium can result in weakness, inappetence, and the risk of heart damage and heart rhythm abnormalities.
There are lots of potential causes of Addison’s Disease. It is frequently called the “great imitator”, as the signs that it causes can also be caused by a myriad of other diseases. Many times, this disease is found by process of elimination or by noticing subtle, nonspecific signs. While nobody wishes to ever find this disease, I would much rather find it that way than in the emergent way. If an animal presents to us on emergency in an Addisonian crisis, it is an emergency that must be dealt with immediately. They are usually very hypovolemic, have heart arrhythmias, and are very depressed and weak. Therapy for these animals involves fluid restoration using isotonic fluids like 0.9% NaCl, which will eventually correct the electrolyte abnormalities. Fast acting dexamethasone should be administered as well, since that is what the patient is deficient in. After the crisis is averted, long term therapy involves glucocorticoid and mineralocorticoid replacement. Glucocorticoids need to be replaced daily, whereas mineralocorticoids can be provided by a monthly injection. Some animals may need extra glucocorticoids provided when times of higher stress are encountered. Once on a treatment plan, most animals will be monitored via blood testing monthly to monitor their disease status and cater their medication dosage to suit their needs.
Once initial treatment is administered and follow-up is provided, prognosis is actually good to excellent for these patients. There are a few causes of this disease, such as cancer or granulomatous disease, that have a poorer prognosis, but these are not the majority of cases. Other endocrine diseases rarely occur in these patients – only about 5% of patients will have concurrent endocrine failure such as diabetes mellitus, hypothyroidism, or hypoparathyroidism.