Actually they've been able to diagnose PD from handwriting.. for a very long time. Apparently one of the early symptoms, which my father got was that their handwriting gets smaller and smaller....
My mother suffered from PD for 17 years. I could tell how she was keeping when I phoned her because her earrings rattled against the handset. When she was feeling well the rattle was soft, but if the PD was bad that day, the rattling was very loud.
I'd like to end things before Parkinson's become truly debilitating. Dementia and Parkinson's, I wouldn't wish that upon the living. I'd rather end it on my terms.