I'm confused by this. It is my understanding that DMDs are not used to treat PPMS. Is it possible that in the instances cited (Rebif and Copaxone), they were prescribed in case it was actually SPMS? (I've read about how SPMS is sometimes mis-dxed as PPMS due to patients not being dxed until they've graduated to that stage, so although progress seems more rapid from the start, it was really that their RRMS did not present enough problems for them to seek a dx.)