My mom has a rescue dog who has been diagnosed with cushies disease. She is doesn't know what that is. I am hearing impaired so the actual name might just sound like cushies. Sam was diagnosed with kidney and liver disease. My mom doesn't want to put him down yet as he is a wonderful watch dog and doesn't appear to be slowing down or in any pain.
I can give you some info on this. Your mom's dog's condition in called "Cushings Disease", but it's also called "Hyperadrenocorticism". Cushing’s is the overproduction of hormones, such as cortisol, by the adrenal glands. The opposite of Cushings is Addison's disease, which is the lower than normal production of cortisol.
Not knowing the dog's current condition, I can tell you that it might not be time to have to think about putting your dog to sleep. If he appears not to be slowing down or in any pain, then he's probably doing okay! While there is no exact life span, it is important to know that the form of Cushing's disease that the dog has. If the adrenal gland was the cause, the life expectancy tends to be about three years. Dogs with pituitary gland issues have a life expectancy of about two years. The younger the dog is when the disease is discovered, the better the life expectancy.
Cushing's Disease has no cure, so control of the disease and symptoms is crucial. Treatment for Cushing's disease involves regulating the hormones produced by the adrenal gland, blood tests should be done about every six months to monitor the medication's effectiveness, so it can be adjusted if needed. It's important to monitor the dog for symptoms. If any symptoms of Cushing's disease appear while the dog is on the medication, talk to your vet. The medication levels will need to be adjusted.
Diets for dogs with Cushing’s disease should be high in protein, which can help to combat muscle wasting as well as being good for the skin and immune system. Fat should be moderately low (less than 12% dry matter), and moderate in crude fiber (8 to 17% dry matter). Avoid giving excessive calcium, as dogs with Cushing’s are predisposed to the development of calcium oxalate bladder stones, due to elevated calcium in their urine. If you think you might change the dog's diet, do so gradually, over a period of 5-7 days, giving your dog increasingly larger amounts of the new food, while decreasing the amount of the old food, until you're only feeding the new diet.
You can read more about Cushings Disease here:
Though it's a very sad thing to have to consider, this site can help you assess when it might be time to think about putting the dog to sleep.
I hope I've been a help. Best of luck,