It definitely exists. A few weeks ago I had to say goodbye to my 14 year old due to severe dementia. He forgot his house training (was physically healthy), was constantly following me around to the point of getting tired, walking circles on the rug without a purpose. He would wander away from us so he had to be on leash at all times. We lost all contact with him. I could have lived with all that if it weren't for the constant peeing in the house.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015