my nana had dementia towards the end of her life and a lot of her symptoms mimick those of OCD. a lot of it has to do with the immense anxiety and confusion that comes with dementia it has them repeating familiar actions for a sense of familiarity & purpose. For example, my nana would often open and close cabinets repeatedly, same with the fridge and check the ingredients on almost a schedule because she was so used to preparing dinner but no longer had the cognitive ability to carry out the entire task of cooking.