PPMS differs from Relapsing/Remitting and Secondary Progressive
in that onset is typically
in the late thirties or early forties,
men are as likely women to develop it and initial disease activity is often in the spinal cord and not in the brain.
Primary Progressive MS often migrates into the brain, but is less likely to damage brain areas than relapsing/remitting or secondary progressive - for example, people with Primary Progressive are less likely to develop cognitive problems.