Secondary progressive MS (SPMS) is a stage that follows for many people diagnosed with relapse-remitting MS.
In this typical later stage, a person will notice a steady decline in mobility despite having fewer or even no relapses. The rate of decline can be slow for some and more rapid for others.
Some people may already be in the SPMS stage by the time they are properly diagnosed. This can be because their previous relapses weren't diagnosed.