I have been in LE for 14 years. In order to be hired, you will have to pass a physical and psychological testing prior to hire. You will also have to endure strenuous physical training and testing during the academy. This will vary from state to state and even from agency to agency. It will also depend greatly on your current physical and cognitive ability. In short, there isn't a one-size-fits-all answer and would likely be decided on a case-by-case basis. I would be very, very surprised if an agency chose to hire someone with MS, though. It's different if you're a veteran officer who becomes disabled versus a new hire (same as with the military).