What Causes Poor Memory And Violent Behavior?

hello i am concerned about my grandfather. i have just been reading about alzheimers and senile dimentia and he has a lot of these symptoms. i have noticed it for over a year now but recently it has been rapidly getting worse. he is forgetting peoples names and faces, even his wife's to whom he has been married to now for 50 years. last week he went to pick her up from bingo and he went missing for over 5 hours. we found him in a car park miles away from where he should have been and he was just sat there crying his heart out. he said he forgot where he was and when we tried to get him to come home he was very violent. he started to shout and swear at us and threatened to call the police. ive tried talking to him about it, but he says he's fine. i dont know what to do!