PD and Parkinsonism / secondary parkinsons

My friend had West Nile Virus 2 years ago, developed encephalitis and awhile later developed the rolling pin shaking left hand. His gate is slow and he shuffles. His doctor said his face had that mask look but said it now looks better now. He has been told he has parkinsonism, secondary parkinsons and post encephaletic parkinsons (3 different doctors, 3 different titles). Last week after being tired, his right hand started to shake for awhile which it hasn't done before. Yesterday morning his speech started to slur for awhile and he lost his balance in the shower.

What we don't understand is the difference between parkinsons disease and secondary parkinsons/parkinsonism. We know it's a known cause. Does it continue to deteriorate the same as parkinson disease? Has all the damage that is going to be done, been done? or will he continue on a downward path? That's where we are confused.