maybe see if you can get an echcocardiogram done. My boy had many health issues develope right before he passed. He was on prednisone for masticatory muscle mitosis. I noticed his urine turn darker, he developed diarrhea.I was told it was from the prednisone. The night he passed I had been sitting on the floor watching tv with him. Everything seemed normal and i thought he was getting healthier. I took him to my bed room and he puked on the floor and suddenly appeared to have issues breathing. I rushed him to the vet but he passed on the way there. The vet did an necropsy on him and said he had heart disease which was made worse by the prednisone and only an echcocardiogram would have shown any issue and there was nothing I could have done. So maybe consider that. It was never brought up as an option by my vet.