“With standard Addison’s disease you have relatively classic findings, and it’s easy to confirm the diagnosis,” says Tufts internal medicine veterinarian Orla Mahony, MVB, DACVIM. “Once you have a reasonable index of suspicion, you should be able to” pinpoint it. But there’s a type of Addison’s disease called Atypical Addison’s, which is a deficiency of just cortisol, not cortisol and aldersterone, “and that may be harder to recognize,” Dr. Mahony explains, “because it doesn’t produce profound changes on routine lab work. Unless you measure cortisol levels in the blood,” which are not regularly measured as part of general laboratory blood screenings, you can miss it.
The clinical signs are somewhat similar to those of classic Addison’s disease — diarrhea, loss of appetite, lethargy, weakness. You may also observe vomiting and weight loss. Blood test signs include elevated white blood cell count, anemia, high cholesterol, and low blood sugar. If that’s the case, and a dog’s sodium and potassium blood levels look normal and all other routine blood screenings check out, the veterinarian may still want to administer an ACTH stimulation test, which can diagnose or rule out Addison’s definitively because it checks to see if cortisol levels rise in response to an outside push from a drug that stimulates the pituitary to stimulate the cortisol-secreting adrenal glands. If the cortisol levels don’t rise, Addison’s is the problem.
Treatment starts out with daily replacement of cortisol with prednisone. No synthetic form of aldosterone is needed, whether as daily pills or monthly injections. But with the atypical form of Addison’s, Dr. Mahony says, “we discuss with the owner that the second hormone may be needed with time.” It’s possible that atypical Addison’s is simply the traditional form of the disease in its early stages, before the adrenal glands give out to the point of secreting insufficient amounts of both cortisol and aldosterone.