Secondary adrenocorticism usually only affects the glucocorticoids. Secondary adrenocorticism probably occurs most often when prednisone or other cortisone being administered for medical reasons are suddenly withdrawn. It can occur as a result of pituitary cancer or some other process that interferes with production of hormones that stimulate the adrenal glands. Most dogs with Addison's disease initially have gastrointestinal disturbances like vomiting. Lethargy it also a common early sign.
Poor appetite can occur as well.
These are pretty vague signs and it is extremely easy to miss this disease. More severe signs occur when a dog with hypoadrenocorticism is stressed or when potassium levels get high enough to interfere with heart function. Dogs with this problem will sometimes suffer severe shock symptoms when stressed, which can lead to a rapid death. When potassium levels get high heart arrythmias occur or even heart stoppage which also is fatal. In some cases, especially secondary Addison's disease, there are no detectable electrolyte changes.