Hi Windyridge,
I never knew that there was a term to describe Dad's endless pacing before, so thanks for the terminology, though it appears to be described a few different ways (including your spelling) when I do a Google search on it. Interesting that your doctor said so certainly that it wasn't caused by the anti-psychotics too seeing as most of the search results I looked at said it often was caused by anti-psychotics. Here's one from Wikipedia for example:
Akathisia, or acathisia, is a syndrome characterized by unpleasant sensations of "inner" restlessness that manifests itself with an inability to sit still or remain motionless..Its most common cause is as a side effect of medications, mainly neuroleptic antipsychotics especially the phenothiazines (such as perphenazine and chlorpromazine), thioxanthenes (such as flupenthixol and zuclopenthixol) and butyrophenones (such as haloperidol (Haldol)), piperazines (such as ziprasidone), antispasmodics (such as metoclopramide), and antidepressants. Akathisia can also, to a lesser extent, be caused by Parkinson's disease and related syndromes.[1] However, most antipsychotic psychotropic drugs cause Parkinsonian like symptoms due to blockage of dopamine receptors in the nigrostriatal pathway of the brain.
That being said, it could also just be caused by the dementia...
As I said earlier, my father also suffered(?) from akathisia, and would pace the halls of the nursing home until he would literally drop from exhaustion, unless he was sat down. One thing to check is whether your Mum can remember how to sit down, because I think part of Dad's problem was that, that he could no longer sit down unless he was guided to a chair and helped to sit down. The fortunate side of that was that he also lost the ability to know how to stand up (it wasn't just because he was old and frail, because Dad was still in his 50s at the time as he has early onset). If she can't remember how to sit down then she may be pacing because she is having difficulty knowing how to do stop.
Despite this, Dad's pacing was manic, I always felt it was a bit like an OCD symptom, because he seemed driven to do it, and would walk to the door, give a little yell, and raise his hands, then turn around and walk to the other end of the hall and do the same at the door at the other end, and back and forth he would go. I put a question mark after the word suffered above, because for Dad at least, I actually took comfort from his walking (except when the nurses at the care home weren't attentive enough to realise that he was nearing exhaustion and needed to be sat down) because it seemed to make him feel better, he seemed to get some calm from the ritual (thus also why I felt it was OCD like). The other thing was, it seemed as if Dad was able to think more clearly if he was allowed to pace, and we often thought it might be because it helped more blood and therefore oxygen be circulated around his brain. Another benefit of the pacing was that he unlike many of his fellow patients has stayed fit, and despite the fact that he has had the disease for 12 years now, and the fact that he cannot feed himself, toilet himself, speak or coordinate any other part of his body to do anything (i.e. he can't pick up objects), if we stand him up he miraculously can walk! If you are a carer at home, this is a great plus because it helps immensely when the patient is so mobile but at the same time cannot wander off if you don't help them to stand in the first place (Dad lives at home again now with Mum).
Of course none of this is reassuring if your mother is appearing distressed by her need to walk, but I mention it in case it is yourself who is more stressed by it. If your mother isn't distressed by the need to walk, but in fact seems happier to do so, then I would suggest trying to make a care plan for her, where she is given time to walk, but that she is monitored so that she isn't at risk of falling. This may be easier said than done however as many care homes are not happy about the time this would require of their staff and thus they often prefer those who are no longer mobile. But if this can be done and it does make her feel better, I would say that that is the best thing for her health and ongoing health.
If the need to walk is distressing her however, I would talk to her doctor again after doing some quick research on the web and printing out some of the information that supports the idea that anti-psychotics can cause this condition and ask him/her again why they are so certain it is not the medications. Sometimes you have to push doctors to consider things outside their experience, and often it helps if you have some documentary support for your concerns.
I would say the greatest risk here is that your mother may fall, and you need her doctor and her care home to help you come up with a plan that can prevent that from occurring. In Dad's case because he was young there wasn't the same kind of risk to bone breakage as an older person faces, so for him we kitted him up with a football helmet and let him walk, but I have seen the damage done to older folks who fall and its not good.
Not sure if I have been much help, but maybe my post will help you think this through a bit more and at least you know your mother isn't the only one who has suffered this problem (by the way Dad used to get an awful lean up too).
Best wishes,