Idk if Parkinson's was the cause,
But I worked with a man whom got a bit scrambled, some days worse than others.
he went to a good doc and after a shitload of tests & referral visits to other good docs over course of months was diagnosed with early onset dementia.
He was in his early 50's, he knew something was up cause he knew we were covering his work that he forgot to complete, and he spoke with us his co-workers & advised his mother's side had cases of early onset dementia,
iircc it took a while before the appointment day with the first doc.