Most people with relapsing-remitting multiple sclerosis -- about 80% -- eventually get secondary progressive multiple sclerosis. The relapses and remissions that used to come and go change into symptoms that steadily get worse. The shift typically begins 15 to 20 years after you’re first diagnosed with multiple sclerosis.
Because multiple sclerosis is such a complex disease, it can be hard to spot the changes that signal SPMS, even for health professionals. Doctors often wait at least 6 months before they diagnose SPMS.