Michael J. Fox was diagnosed with Parkinson's disease in 1991, and he continued to act on the show "Spin City" for several years after his diagnosis. He left the show in 2000, and Michael Boatman replaced him as the main character.
Charlie Sheen has had a long and varied career in television, but he was not involved with "Spin City". He is best known for his roles in shows like "Two and a Half Men" and "Anger Management".