Approximately 10 percent of people with MS experience a primary-progressive course. For them, the disease progresses fairly steadily from the beginning, without any relapses (also called attacks or exacerbations) or significant remissions. However, the rate of progression differs from one person to another and over time for any single individual.
Although there is a lot of variability among people with PPMS, we know that as a group, they differ in several ways from people with relapsing forms of MS:
- Relapsing MS is defined by inflammatory attacks on myelin. PPMS involves much less inflammation of the type seen in relapsing MS. As a result, people with PPMS tend to have fewer brain lesions (also called plaques) than people with relapsing MS, and the lesions tend to contain fewer inflammatory cells. People with PPMS also tend to have more lesions in the spinal cord than in the brain. Together, these differences make PPMS more difficult to diagnose and treat than relapsing forms of MS.
- In the relapsing forms, women are affected 2-3 times as often as men; in PPMS, the sex ratio is 1:1.
- The average age of onset is approximately 10 years later in PPMS than in relapsing MS.
- People with PPMS tend to experience more problems with walking and more difficulty remaining in the workforce.
- In general, people with PPMS may also require more assistance with their everyday activities.
- For a visual illustration of how PPMS differs from other forms of MS, please explore our information about the four disease courses of MS.