Addison’Desease - Hypoadrenocorticism
Hypoadrenocorticism, also commonly called Addison's Disease, is the failure of the adrenal gland to produce corticosteroids. It is currently felt that an autoimmune or an idiopathic disturbance leads to the inability of the adrenal gland to produce corticosteroids. Most dogs initially diagnosed with the disease are between 2 and 7 years of age. This is a relatively rare disease with a prevalence of approximately 1.8 cases per 1000 dogs.
Clinical Signs and Diagnosis:
Dogs with hypoadrenocoticism frequently present with vague clinical signs. There is frequently a history of intermittent vomiting, diarrhea, and weight loss. Frequently these dogs have responded to prior treatment with fluid therapy or a steroid.
Veterinarians are classically presented with a young animal in shock. There is usually no history of trauma or toxic exposure so general treatment for shock is initiated. This consists of rapid administration of fluids (usually lactated ringers solution, which has little potassium and a moderate amount of sodium) plus some glucocorticoids. By coincidence, this also happens to be similar to the specific treatment for Addison's disease so that often the patient simply recovers without the veterinarian really knowing why.
The blood panel will come back showing elevations in the renal parameters (BUN and Creatinine) and thus with the elevated potassium is suggestive of acute renal failure, a condition with an extremely poor prognosis. The veterinarian may become suspicious of another diagnosis as the patient will respond well to fluid administration and most renal failure patients do not respond as well.
Addison's disease may present in more unusual ways. Inability to maintain normal sugar levels (ultimately manifesting as a seizure disorder) may be strongly suggestive of an insulin-secreting pancreatic tumor but before a major abdominal surgery is planned, it is important to test for Addison's disease.
Similarly unexpected, regurgitation of undigested food due to abnormal nerve function in the esophagus (a condition called Megaesophagus) can be caused ultimately by Addison's disease.
Because of the numerous symptoms Addison's disease can be present with, Addison's disease has earned the medical nickname "the Great Imitator." The only definitive test for Addison's disease is the ACTH stimulation test. The patient receives a dose of ACTH, the pituitary hormone responsible for the release of corticosteroids in times of stress. A normal animal will show an elevation in cortisol in response to ACTH while an Addisonian has no corticosteroids to respond with. This lack of response is diagnostic for Addison's disease; however, a false positive may be obtained if corticosteroids have been used in the treatment of the crisis prior to the test. Only dexamethasone does not interfere with the assay for cortisol; if any other steroid has been used, the test will not be valid for at least a couple of days.
Treatment After The Crisis:
The most important aspect of treatment for hypoadrenocorticism is the replacement of the missing mineralocorticoids hormones. One way to do this is with oral Fludrocortisone Florinef. Florinef is given usually twice a day at a dose determined by the patient's sodium and potassium blood tests. At first, these electrolytes are monitored weekly. When levels seem stable, these blood tests are repeated 2 to 4 times per year. Often with time, it will be found that the dose of Florinef needed to control the Addison's disease will increase. This is unfortunate as the medication is relatively expensive. Since Florinef has glucocorticoid activity as well as mineralocorticoid activity, it is not necessary to use additional medications for treatment.
Another way to treat this condition is with an injectable medication called DOCP (brand name Percorten-V). This treatment is given approximately every 25 days. Electrolytes are measured prior to injections at first but testing can usually eventually be tapered to once or twice a year. There is some feeling among experts that DOCP produces better regulation of electrolytes than does oral Florinef. Some dogs however, do require glucocorticoid supplementation (such as a low dose of prednisone).