Like anything that causes prolonged hyperglycemia, one of the side effects over time can be permanent diabetes. Some causes of Cushing's are pituitary or adrenal gland tumors and overuse of glucocortoid steroids. When dealing with concurrent conditions of both Cushing's and diabetes mellitus, the diabetes needs to be under some sort of control and any DKA resolved before testing for Cushing's Disease can be done. Another disorder of the adrenal gland causes it to produce less than normal cortisol. It is known as Addison's disease and is the direct opposite of Cushing's disease.