Addison's Disease, or hypoadrenocorticism, is a syndrome resulting from a deficiency of cortisone hormones normally produced by the adrenal gland. Cortisone-type hormones have numerous effects throughout the body and are essential for life. Addison's disease is uncommon in dogs, but we typically see several cases per year. The disease is rare in cats.
Addison's Disease occurs when the body's immune system attacks the adrenal gland, resulting in destruction of the gland. The cause of this immune-mediated destruction is unknown. Other endocrine diseases, such as hypothyroidism, likely occur by a similar mechanism. In fact, it is possible for two or more endocrine diseases to coexist.
A second form of hypoadrenocorticism can occur. Steroid medications such as prednisone are commonly prescribed for a variety of conditions, but especially for itchy skin and other allergic reactions. Because oral steroid medications are so similar to the cortisone naturally produced by the adrenal glands (albeit a higher dose), the adrenal glands begin to atrophy because the body does not need any more cortisone. If steroid medication is given for a long period of time (weeks to months), the atrophy of the adrenal gland can be severe. If the medication is abruptly stopped, the adrenal gland is unable to start producing cortisone immediately, and symptoms of hypoadrenocorticism can appear. This is why patients on long-term steroid medication should be tapered to as low a dose as necessary — ideally only given every 2-3 days (depending on the specific medication). This "Alternate-Day" dosing regimen helps prevent the adrenal gland atrophy that could cause problems when the medication is stopped. Ideally, cortisone medication should be gradually tapered when the patient is ready to come off.
Most dogs with Addison's Disease are middle-age and older. Female dogs seem to be more prone to the disease than males. Predisposed breeds include the standard poodle, Airedale terrier, basset hound, bearded collie, Great Dane, springer spaniel, and West Highland white terriers.
Early symptoms of Addison's Disease can be vague and non-specific. Affected patients tend to have intermittent episodes of poor appetite, lethargy, vomiting, or diarrhea. Owners often attribute the symptoms to "stomach flu" or any number of other common conditions. Symptoms may worsen during periods of stress such as boarding in a kennel. The symptoms mentioned above resolve on their own or with simple treatment, only to recur at a later time. As the functionality of the adrenal gland worsens, the symptoms tend to become more frequent and severe. Some patients develop a condition called an "Addisonian Crisis," which is a medical emergency. This crisis is characterized by severe lethargy, weakness, dehydration, hypothermia, and weak pulse. Patients can easily die if diagnosis and treatment are not rapid.
Blood tests are important in the diagnosis of Addison's Disease. One characteristic feature is a severely high blood potassium concentration, which can be easily tested in-house at a quality veterinary hospital. Confirmation of the disease is made by an ACTH Stimulation Test — a specialized blood test that must be sent out to a reference laboratory. When history, symptoms, and initial bloodwork suggest Addison's Disease, it is appropriate to begin therapy for Addison's Disease. Since final confirmation requires 1-3 days, this is too long to wait to begin treatment for those patients presenting as an emergency. Some patients have a more atypical form of Addison's Disease, where classic electrolyte (sodium, potassium, and chloride) abnormalities are not present. These can pose more of a diagnostic challenge — especially early in the course of the disease when routine bloodwork may be normal.
Animals presenting as an emergency require immediate fluid therapy. Fluids are typically administered rapidly to help correct severe dehydration and electrolyte imbalances. Aggressive fluid therapy by itself can be lifesaving, although steroid medication is typically begun soon after blood samples have been drawn for testing (certain steroids can interfere with diagnostic testing). Steroid supplementation must be continued lifelong since the body is unable to manufacture its own. Most patients tend to respond quickly to proper treatment, although some can still be quite sick for several days.
Although a very serious disease, Addison's Disease is rewarding to treat because of the profound improvement achieved with proper treatment. Many owners are amazed at the improvement in quality of their pet's lives; because early symptoms are often so gradual and intermittent, owners may attribute many changes in their pet as simply "getting older."
Two medications are available for the long-term management of Addison's Disease. Fludrocortisone acetate is an oral tablet usually given twice daily. It is an excellent cortisone supplement that quite effectively manages this disease. Another option is desoxycorticosterone pivalate (DOCP), which is an injection given every 25-30 days. DOCP is also quite effective. At this time, both drugs appear to be equally effective. The choice comes down to personal preferences of the attending veterinarian and personal wishes of the owner. Those owners having difficulty giving pills would likely prefer the injection, while those owners who prefer not to travel to the veterinarian every 4 weeks would likely prefer the tablet. We prefer using fludrocortisone acetate tablets. We like the flexibility that an oral medication gives — especially when first beginning treatment. Dosages can easily be increased or decreased based on follow-up blood tests.
Some patients benefit if also medicated with oral prednisone in addition to one of the two above medications. Some patients have loose stools on occasion or do not eat well, and the addition of prednisone can be beneficial in these cases.