Unfortunately most of the actors that have come out about their diseases have had to because it shows, Michael J Fox (Parksions), Christopher Reeves (spinal Cord injury), they couldnt hide it .Other diseases because they wanted to take a stand on the them like Montel Williams, (he was a big enough star that he knew it wouldnt hurt his carrer) as was Marry Tylor More.
Look at how long it took the Stars to come out to say they were HIV Pos or has Aids.
Being Ill hurts there carerrs. People dont want to hire them if they are sick and dont feel good some days or will get worse as sometimes in PN. And most people dont know what PN is so they wouldnt have that empathy that alot of other diseases cause their fans to feel for them. It would have to be a brave person to say they have PN and then see how much work they got if it got worse, went from walking to walking with a cane to being in a wheelchair, so they may not want to show what they have because the people that hire them might go with someone "healthy".
Im sure there are actors out there that just dont want to loose their livelyhood and speek out on this. I cant judge them but maybe some brave person will do it.