Acute onset of dementia - looking for answers!!!?

My dad has had two recent acute 'events' of dementia. The first one lasting on a few hours, 2nd time lasting much longer - from 7 am until 5 or 6 that evening. He spent the day in the hospital and left w/out a diagnosis. During these 'spells' his short term memory is non-functioning. He will ask the same questions over and over, make the same 'jokes' or comments over and over and not realize he's already said it. During his health history he heard my mom tell the nurses that his mom had passed away a year ago, and it struck him as though it was the first time he'd heard. He 'forgot' that my sister was pregnant and due in 5 weeks, and he looked shocked when he saw her in the hospital that day, asking her when she was due. He has no problem with recognition. We're all confused. The bloodwork, echo, dopplar, and eeg are normal. The MRI was unremarkable and he's to see a neurologist this week. Any ideas?

The Dr referred his 'spells' as dementia. He's confused, knows family etc, but doesn't know the date, month, year, etc, or who is president.

So what you're saying is that short term memory is bad, but long term is not bad. That's why he can still speak english, can still recognize immediate family, and so on - long term. But recent stuff, in the last year or less than 9 months, is obviously not.

I don't know - is this "dementia" as in losing it and going senile, or some other form of brain problem relating to memory?

Has he been started on any new medications? Drug interactions are a very common, often under-recognized cause of confusion symptoms in the elderly.

I doubt that he is demented. Dementia does not come on acutely. By definition a dementia is a decrease in mentation from baseline but it is a gradual process. The only exception is a vascular dementia that can come on suuddenly but the MRI would pick this up. Altered mental stae may be due to a delirium where the patient may return to normal in between. There is a condition called "transient global amnesia" where the patient may be functioning normally and then ask the same question repeatedly and after a few hours return to normal and he had no recollection of what happened. The etiology of this condition is unclear. It may be epileptic or a TIA. This is probabaly what he had if he is back to normal.