Alzheimer's and Parkinson's is often preceded by concussive injuries like car accidents and repeated football concussions. When my 3000GT got totalled by a drunk driver I noticed some memory slippage in myself.

When I was researching various brain diseases last year one of the traits was inflammation and I realised in many cases it was the inflammation from the other injuries that was the prime mover to the disease. It is no surprise that any injury from disease or accident that causes inflammatory injury to the brain can lead to neurodegenerative diseases. That being the case effective treatment of the inflammation should at minimum stop disease progression and may be able to reverse it to some extent.