My husband is losing ability to digest food as well as "mess his pants." Is this part of advanced Parkinson's Dementia?

This may well be progression, but we also have a tendency to chalk everything up to the disease at hand, so try to rule out other changes. Has he had to take any antibiotics of late? That could disrupt the normal flora, and could even lead to the dread C-Diff, something that the strongest of us cannot "hang on to". Is there a change in his diet. For instance are you adding supplementals like milkshakes or ensure or some such which has a lot of lactulose problems and makes things difficult. Sometime things like citrucel and metamucil help, but hard to take in powder form as hardens before they can get it down and capsules are often too large. As well as being good for constipation they help form bulk in stools and are good for diarrhea. Metamucil ferments a lot and is digested differently than citrucel, so I definitely recommend citrucel be the choice. Otherwise the gassy stuff can make a bad problem worse. Does he say he is unable now to clearly tell when he needs to go? Try to sleuth around a bit, and then report to doctor. Take in a stool specimen so they can run it through and be certain nothing shows up that could be treated. Wishing you good luck.

I am so very sorry you and your husband are having to ensure this. My Dad has FTD (type of dementia closely related to ALS, Lou Gherig's Disease) with some "Parkinsonian features" and it has helped me to learn what to expect as he progresses through the stages. The end stages are heartbreaking to contemplate, but it has helped me prepare.

This looks like a list of lot of good resources for you:

http://parkinsons.stanford.edu/latestagePD.html

Wishing you the best through this terrible trial. Please let us know how you are doing!