By Adam Brimelow
Health correspondent, BBC News
More than 400,000 people in the UK have Alzheimer's disease
Further research is needed into a US treatment for Alzheimer's disease that appears to produce marked improvements in some patients, experts say.
California researchers believe they have found a way of improving brain cell communication by injecting a drug called etanercept into the neck.
The Institute for Neurological Research team has described changes taking place in Alzheimer's patients within minutes.
British experts have expressed caution, but say further research is merited.
More than 400,000 people in the UK have Alzheimer's disease.
Current medication can slow the disease, but charities say there is a desperate need for research to develop more effective treatments.
Doctors in California have devised a novel approach, injecting anti-arthritic drug etanercept into the neck, and then tilting the patient to encourage blood flow into the brain.
About 50 people are being treated at the private clinic.
Some have been taking etanercept for more than three years. Doctors report a response rate of about 90%, usually within minutes.
They say typically they see a week-by-week improvement with each dose, reaching a plateau after about three months.
Professor Edward Tobinick, who leads the research, said: "What we see is an improvement in their ability to think and calculate, their memory improves, their verbal ability improves, they find words easier, they seem happier, and we often also see an improvement in gait in those patients whose gait is affected."
But he warned they did not return to normal.
In video footage, supplied and edited by the clinic, a nurse sits down with 82-year old Marvin Miller, who frowns and mumbles incoherently as she asks him a series of basic questions.
He fails to recognise everyday objects including a bracelet and a pencil. Shortly afterwards he is injected with his first dose of etanercept.
Five minutes later - according to the footage - he greets his wife, who stands visibly shocked, saying he has not recognised her for years.
Mr Miller then embraces her.
In a separate interview, again supplied by the clinic, she describes his improvements four weeks later.
She says he makes sense 90% of the time now, compared with none of the time before treatment started.
Etanercept is not a new drug. It is a widely used treatment for arthritis, blocking a chemical called tumour necrosis factor-alpha, or TNF, which causes pain and swelling in the joints.
TNF may also affect communication between brain cells - and could be partly to blame for the advance of Alzheimer's.
The researchers in Los Angeles believe they have discovered a way of delivering etanercept into the brain via an injection in the neck, allowing it to block the disruption caused by TNF.
However, many experts are sceptical.
The numbers involved are very small, and crucially, there has never been a placebo-controlled study.
But Dr Suzanne Sorensen, head of research at the Alzheimer's Society, said there was growing interest in this new approach.
"We haven't heard any realistic accounts of people improving that much. And that is why when we first heard about it in January I didn't really believe it to be honest.
"But we have now seen film footage of people improving remarkably very soon after having been given the drug and many more people have now been treated with this drug. So I think it is the time to run a small clinical trial."
Professor Clive Holmes, of Southampton University, said he was willing to take this on, although funding had yet to be secured.
"I think the evidence that's coming through from basic science would suggest to me that there is now a point at which it's worth giving these drugs a trial to see if there is any evidence on a larger scale basis".