People are often confused by the terms primary and secondary and the relationship between these two disease courses. Although both are considered progressive courses of MS, one does not follow the other. And, they differ in several important ways.
- SPMS occurs in people who initially had a relapsing-remitting disease course. In other words, SPMS occurs as a second phase of the disease for many individuals. PPMS is the first — and only — phase of the illness for approximately 10% of people with MS.
- In SPMS, people may or may not continue to experience relapses (also called attacks or exacerbations) caused by inflammation; the disease gradually changes from the inflammatory process seen in RRMS to a more steadily progressive phase characterized by nerve damage or loss. People with PPMS never experience any relapses.
- While many of the approved disease-modifying therapies may be effective in some people with SPMS, none of these medications have been shown to be beneficial in PPMS.
Secondary-Progressive MS follows an initial period of relapsing-remitting MS (the most common form of MS in people who are newly-diagnosed). In SPMS, the disease begins to worsen more steadily, with or without occasional attacks, slight remissions, or plateaus.
Primary-Progressive MS is characterized by steadily worsening neurologic function from the beginning. Although the rate of progression may vary over time — with occasional plateaus and temporary, minor improvements — there are no distinct relapses (also called attacks or exacerbations) or remissions.
- For a visual illustration of how SPMS differs from PPMS, please explore our information about the four disease courses of MS.