How chronic diseases can affect personality?

Parkinson's Disease

While it might start as a little shakiness in your hand, Parkinson's can eventually affect how you walk, talk, sleep, and think.  Even early on, it can lead to things like obsessing over small details or a sudden carelessness. Later, you may seem absent-minded or not as social as you used to be. And it gets harder to keep your thoughts going in one direction.