An injection that dramatically relieved the symptoms of Alzheimer's disease within minutes would qualify as the discovery of the decade. That is exactly what was claimed yesterday for an experimental treatment being tested in America.

Scientists at the Institute for Neurological Research at the University of California have treated around 50 patients at a private clinic by injecting an anti-arthritic drug, etanercept, into the spinal column in the neck and then tilting the patients to encourage the drug to flow to the brain.

They claim 90 per cent respond to the treatment, usually within minutes, and have released videos of patients to prove it.

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In one, a nurse sits down with an 82-year-old patient, Marvin Millar, who frowns and mumbles incoherently as she asks him identify everyday objects such as a bracelet and a pencil, which he is unable to do.

But five minutes after being injected with etanercept – according to the film which was supplied and edited by the clinic – he greets his wife. Visibly shocked, she says he has not recognised her for years. Mr Miller then hugs her.

In a separate interview, also supplied by the clinic, she describes his improvements four weeks later, saying he makes sense 90 per cent of the time now, compared with none of the time before treatment started.

After the BBC reported the claims yesterday, callers jammed the Alzheimer's Society's helpline demanding details of the treatment.

Experts urged caution, warning that the drug had been tried on only a very few patients and, crucially, had not been tested against a placebo in a randomised controlled trial.

Etanercept is not a new drug, but this is a novel use of it. The California researchers injected it between the cervical vertebrae at the back of the neck, just below the skull, directly into the spinal column. Tilting is thought to encourage the drug to cross the blood-brain barrier. In arthritis, the drug blocks a chemical – tumour necrosis factor-alpha (TNF) – which causes inflammation and pain in the joints. It is thought TNF may also influence inflammation in the brain, and that by damping down the process the drug may preserve brain function.

Professor Edward Tobinick, who is leading the research, said: "What we see is an improvement in ability to think and calculate, memory improves, verbal ability improves, [patients] find words easier, they seem happier and we often also see an improvement in gait in patients whose gait is affected."

The researchers said improvement usually continued with weekly injections until it reached a plateau at about three months. Some patients had been taking it for three years. But they have only published details of 15 patients in a pilot study.

An estimated 400,000 people suffer from Alzheim-er's disease in the UK and claims for new treatments are seized upon by relatives, desperate for any straw to clutch. Suzanne Sorenson, head of research at the Alzheimer's Society, said she had been sceptical of the claims when she heard about them in January but having seen the film foot-age, considered it was now time to run a trial.

"On the surface these results are exciting but we need to treat the study with caution," she said. "There are large gaps in the resear-ch, which used a small pilot group. We cannot draw conclusions until a controlled trial is carried out."

Clive Holmes, professor of biological psychiatry at Southampton University, a centre for research on dementia, said he was prepared to test the drug.

"The evidence from basic science suggests it is worth giving these drugs a trial to see if there is evidence on a larger basis," he said.

The elusive search for a cure

*A hundred years after Alzheimer's disease was discovered, a cure for the progressive neurodegenerative condition remains a distant dream. Despite dramatic breakthroughsin other areas, there has been little to celebrate in Alzheimer's. The main advance has been drugs to control symptoms such as agitation and restlessness. But restoring memory and cognitive ability has proved much harder.

The condition is caused by an accumulation of protein deposits in the brain which produce the symptoms of dementia.

There are three drugs with claims to halt the disease's progression (though not reverse it), Aricept, Reminyl and Exelon. In 2005 their NHS use was restricted to the moderate stage of the disease – as opposed to early or late stages – by the National Institute for Clinical Excellence because of their limited effect.