Should you tell or not?

Well, not knowing what to do, I told my mom about it. In the beginning stages she said, "oh, there's nothing wrong with me. Everyone forgets in old age. It's normal." So I didn't press the issue... But now in mid-stage, I have told her and she vehemently denies anything is wrong with her. So, honestly, I guess in a beginning stage it's "iffy" to tell or not tell (i.e. when they are capable of comprehending the diagnosis if they want to make arrangements, etc) but once they hit mid-stage there's no point in discussing or unveiling the diagnosis because they are no longer able to really understand what is wrong with them, and in many cases, you are the bad guy for telling them and are lying to them in their eyes. It only upsets them at this point.