Why is my grandmother experiencing severe short term memory loss when tia, stroke ruled out?

Possibly Alzheimer: Grandma could possibly have the beginnings of alzheimer's DX or even more probable is the beginning of senility; a narrowing of the cerebral blood vessels.

Atherosclerosis?: Dr. Goldsmith is quite correct: it could be the early onset of alzheimer's disease (can be diagnosed); though tia's( transitory ischemic attacks) & strokes may have been ruled out; narrowing of the cerebral circulation from atherosclerosis is common at this age, & a likely reason for the problem. A TIA need not have occurred, but surely the narrowing of blood vessels can reduce cerebral function.