Symptoms of Alzheimer's disease may be detected fully two decades before sufferers begin to experience memory loss, Swedish researchers said on Wednesday.

Inflammatory changes in the brain that activate dial cells in the central nervous system could "greatly influence the development of the disease," researchers at Karolinska Institutet in Stockholm said.

"This study increases our understanding of the early stages of Alzheimer's disease," Agneta Nordberg, a professor at Karolinska and co-author of the study, told daily newspaper Dagens Nyheter.

The study, published in the neurology journal Brain, detected the symptoms by studying families of people with known Alzheimer's mutations through memory tests and gamma-ray scans.

The early traces of the disease uncovered by the study show that "it should be possible to provide early prophylactic or disease modifying treatment," the researchers said.

Nordberg said previous research has focussed on the presence of amyloid proteins but largely failed to propose treatments, "perhaps because most studies have been carried out on patients who already have explicit symptoms."

"This discovery shows that there are other components that are just as important to study," Nordberg said.