In animals with Addison's disease, there is a deficiency of the corticosteroid hormones. At first signs are very vague - listlessness, possibly some vomiting or diarrhea. The animal collapses in shock due to its inability to adapt to the caloric and circulatory requirements in stress. Blood sugar may drop dangerously low. Potassium levels soar and disrupt the heart rhythm because there is not enough conserved sodium to exchange for potassium.
Heart rate slows, arrhythmias result.
The patient may not survive this episode. 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 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. 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.