Interesting (observational) study headlined by Yahoo and USA Today ... today (June 25, 2019) citing a study of out of the UK (U of Nottingham) finding a link between dementia (and probably its various varieties) and some anticholingeric drugs sometimes prescribed by physicians for certain types of PD patients. Basically these drugs are neurotransmitter blockers, which may or may not be a good thing depending on the individual's "rigidity" and its severity. They obviously can help some PD patients suffering from this situation.
I'm not a physician nor a neurologist, but my guesstimate here is that PD eventually leads in many cases to neurotransmitter damage regardless of almost anything some PD patients and their physicians can do. Is this situation (dementia risk) a "flip of the coin" for some PD individuals?
Probably. It is the standard trade off we find all the time, at least most of the time.
Since some of these AC drugs are more risky than others, check with your physician if you are taking one that he/she is prescribing one that presents the lesser risk.