Hi I Had A Mri It Looks Like M.s But

Hi I had a mri it looks like m.s but when I had spinal tap it came back no lyme no m.s. Now the docter suggested that I take ondansetron for fibermialgia symtoms because he says the symtoms I'm having are the same as a person with fibermialgia I have spots on my brain so I ask him if a person with fiber .... Would have spots on brain he says no so why should I take this med