dog losing muscle mass, Cushings disease?

[Hogansma]

My 10 year old dalmatian, Molly is losing muscle mass all over and has recurring diarrhea. She has been on 5 mg of prednisone daily since age of 6 months and the vet suspects maybe Cushings disease. Is diarrhea a symptom of Cushings? She eats well but doesn't gain weight. The muscles in her face, chest, legs, hips are wasting away. The vet just treated the diarrhea last time with flagyl pills and pepto bismol. It seemed to work but never found the cause. I am going to make an appointment tomorrow for her. Last night she had diarrhea all over the house. I spent hours cleaning her, her brother, plus the house too. Has anyone had a similar experience with muscle loss and diarrhea?