I'm so sorry to hear about the person you know who has Parkinson's. Hope he will find the help he needs & isn't too uncomfortable.
Way back in 1974 - my sister Flo, then aged 41, had a brain tumour removed. She eventually recovered from that & went on to pass her driving test just before her 50th birthday!
However, some years later, she was diagnosed as having the dreaded Parkinson's disease, which was an awful shock to her & all the family. She is now in the advanced stages of it, but is on medication & 'somehow' manages to get thro' each day. She still has a kind word & a smile for everyone, even tho' life can be a struggle for her at times.
She was once offered some kind of medical procedure on her brain to alleviate some of the PD symptoms, but declined, as it was relatively new & she didn't want to take any chances.