Is “explosive diarrhea” a part of Parkinson’s dementia?

Just been seeking answers to my own mothers diarrhoea and she has IBS and diabetes. The diarrhoea became explosive and she had black streaks in it, very sticky. Turns out the Maxolon she was prescribed for nausea is 4 times as likely to cause diarrhoea if you have PD. Also has gastroparesis due to her diabetes. Antidepressant has stopped nausea.

The protein (alpha-synuclein) whose misfolding is associated with PD is also found in the gut.and may appear there before it is found in the brain. (Some forms of) this protein have inflammatory properties and, I believe, can cause or initiate microscopic colitis. Your Mom needs to see a gastroenterologist and have a colonoscopy. If this conforms colitis they will probably prescribe budesonide, a synthetic steroid that controls colitis very effectively and can be taken long term.
It works well for me!

My mom has PD without Dem. I have never heard that these two things are related. Call her doc immediately. Chronic diarrhea can cause other problems like dehydration and an imbalance of other nutients. She may have an intestinal bug.

Has she had a change in medications lately? Some can have this effect.

Normally, in a healthy person, I would recommend letting the bug work itself out naturally through their system. But when you are dealing with an elderly person, things can get serious fast.
good luck