My 83 year old father had shingles (trunk) 3 months ago, and appears to be experiencing the same thing as your mother, although perhaps more mildly at this point. It presents as memory loss & distortion, confusion, anger and agitation, and other personality changes. It is mild enough in some ways that people who know him less well, or don't spend much time with him, don't notice much difference. It is variable over time, but with no sustained improvement, and is probably slowly worsening (?). Brain scans are normal.
Facial/ophthalmic shingles, I believe, may be associated with either a viral extension involving the brain itself, or perhaps purely an inflammatory (but sterile or non-viral) meningo-encephalitis, with associated mental changes. I'm not sure of the natural history of this, and could find only 1 or 2 articles referring to it (Medline/PubMed).
I have been told, second hand, the apparently anecdotal experience of an experienced geriatrician that some older people, especially those already experiencing "normal" age-related mental decline may, with Shingles or any other systemic insult, experience a rather precipitous decline further decline which usually does not improve. I can find nothing to confirm or expand this observation in the medical literature (Medline/PubMed).
Anyway, our experience seems similar to yours' and may be an example of what the geriatrician was talking about.
