My dad had vascular Parkinsonism for 42 years. His neurologist recognized that his symptoms started after being struck in the head with a steel cable, and that he had multiple infarcts throughout his brain. He was kept off L-dopa for 41-3/4 years.
But his doctor of many years quit to do research and a new, busy doctor took over his case. He couldn’t imagine a patient who wasn’t on L-dopa, so on it Dad went. In less than a week he had “frozen” smooth muscles along his urinary tract. He promptly needed a cathater, and he developed an infection. With the infection came psychological issues. He couldn’t remember why the catheter was there and kept pulling it out, making the infection worse and worse. He died of sepsis from that bladder infection about three months after going on L-dopa.
The caveat in the story for most PD patients is that my father’s disease was of vascular origin. But L-dopa can go very badly.