The underlying cause of the liver disease will dictate the type of treatment. Mild forms of disease can be treated medically with pharmaceuticals designed to reverse the damage to the liver. In more severe cases, involving chronic disease or cancer, surgical intervention may be an option. Because liver disease affects so many parts of the body, medical management of all symptoms is important.
Liver disease is considered "somewhat to very" painful so it's important to talk about this with your veterinarian!