by Jennifer Chaitman, VMD, ACVIM (Internal Medicine) and Eveline Han, ACVIM (Internal Medicine)
Hypoadrenocorticism, or Addison's disease, was first described in people by Thomas Addison 150 years ago. It is a condition resulting from lack of adrenal hormones. In people, it is caused by immune-mediated destruction of the adrenal glands. An immune-mediated cause is suspected in the dog as well. Addison's can also occur as a result of treatment for hyperadrenocorticism (Cushing's) with mitotane (Lysodren, OPDDD).
The adrenal glands are a paired organ and live next to the kidneys. They are essential for life. Glucocorticoids, mineralocorticoid, sex hormones, and catecholamines are all made by the adrenal glands. With Addison's disease there is a lack of glucocorticoid and mineralocorticoids. Glucocorticoids have many effects, including blood glucose regulation, fat metabolism, protein metabolism, and water balance. Therefore, a lack of glucocorticoids results in low blood sugar, weakness, vomiting and diarrhea. Mineralocorticoids are responsible for maintaining blood volume by regulating sodium and potassium. When there is a lack of mineralocorticoid, potassium levels can become dangerously high and sodium levels can become dangerously low. An Addisonian patient is at risk for severe dehydration and low blood pressure. This can also lead to kidney failure.
The signs of Addison's disease are non-specific. Commonly, dogs are sick on and off for months with vomiting, weakness, and lethargy. They may get sick after a trip to the groomer or when stressed by some other factor. Some dogs may just tremble, others may have seizures.
Diagnosis of Addison's disease rests mainly with blood tests. The blood tests frequently show high eosinophils and lymphocytes (types of blood cells) and low serum sodium and high serum potassium. Occassionally, hypercalcemia (high blood calcium level), or low glucose (blood sugar) may be seen. There can be poor function of the kidneys due to the resulting low blood pressure and reduced fluid volume to make urine. Because cortisol functions as a "permissive" hormone to the actions of other hormones (epinephrine, thyroid), a low level of cortisol can result in poor heart function, gastrointestinal motility, and skin conditions. If an immune mediated mechanism is responsible for the Addison's disease, then it is an occasional problem to see an attack on other glands in the body such as the tear (lacrimal) glands and thyroid gland. On occasion Addison's disease may initially be discovered when a "crisis" or shock like episode occurs. This requires emergency care. Testing for Addison's disease is done by use of an adrenal gland stimulation test (the ACTH stimulation test). Rarely, only poor cortisol production is seen (atypical Addison's disease) while aldosterone production remains normal.
Initial treatment for Addison's may include aggressive fluid therapy to correct dehydration, prednisone (a glucocorticoid), and florinef (a mineralocorticoid). Prednisone is given in tiny physiologic doses, so the “bad” side effects of prednisone are not seen. Your doctor may recommend monthly injections of mineralocorticoid (DOCP) instead of florinef because it is somewhat less expensive. However, this will require monthly trips to the vet, or you can learn to give the injections yourself at home.