When dementia doesn’t look like dementia it might be something else.
Persons who are widely fluctuating in their cognitive presentation, going from perfectly oriented with no significant memory impairment to having profound delirious or psychotic episodes, and having the usual suspects (e.g. UTI) ruled out, in my professional experience probably have something else.
It could be a brain tumor or the effects of an old stroke on the frontal lobe. Accurate diagnosis is critical for appropriate treatment.