No they won’t. The point of the existing DMDs is simply to reduce the inflammatory process which causes relapses.
In PPMS there are no relapses.
Therefore a DMD which prevents relapses will not work on a person who actually has PPMS. Or in fact SPMS. Unless they have SPMS but continue to have relapses. Which is the reason why many neurologists keep a person officially labelled as RR when they’ve really become SP. But you should remember, the neurologists are doing this. They are not being ‘conned’ or treating someone irresponsibly. They have good reasons for what they do and they will stop prescribing once they see there is no value to the person.
In the past, I have taken 4 DMDs when I was RR. I experienced severe side effects from three of them:
Avonex caused very bad cognitive problems. This was in 2002. I did not at that point have any cognitive problems. I did not recognise the side effect for 4 months. In that time I was confused by so many things. I did my job very badly. I was confused by the symbols on my cooker. No it wasn’t actually dangerous to my health, but did me no good whatsoever.
Tysabri gave me severe hepatitis. Fortunately, the liver is a very resilient organ. It recovered.
Tecfidera gave me Lymphopenia. This is fairly common. It reduces the white blood cells that fight viruses. It recovered within a year. Very low lymphocytes leave a person vulnerable to any viruses they encounter.
Only Copaxone did not give me bad side effects. Only Copaxone did the job of fighting relapses. Eventually it stopped working and I suffered a number of severe disabling relapses. I am now a full time wheelchair user.
There are many other serious side effects possible from other DMDs. There are people who have died due to side effects. People who have become badly disabled by side effects. Many DMDs require a consent form to be signed in which you state that you accept the possibility of severe side effects. They are not drugs to take lightly. And they are certainly not drugs which a person should take for the sake of it.
And advising a person to deliberately lie to a doctor is irresponsible at the very least. When someone is recently diagnosed with MS, they are living with new symptoms, a potentially frightening prognosis and they may well accept the guidance of someone who they assume to know the best thing to do.
This is obviously my opinion, you should do as you think best.