A new type of dementia has been identified by an international team of researchers, BBC reported.
The newly identified condition - limbic-predominant age-related TDP-43 encephalopathy, or LATE, shares similar symptoms to Alzheimer's, but it is a distinct disease, the journal Brain reports.
LATE appears to be linked to the accumulation of a certain protein, TDP-43, in the brain, while Alzheimer's is linked to two other brain proteins - amyloid and tau.
Millions of elderly people have a form of dementia that has been misdiagnosed as Alzheimer's disease. The new discovery is the most important dementia finding in years, some experts claim.
It may partly explain why finding a dementia cure has failed so far.
Dementia is the name for a group of symptoms that include problems with memory and thinking. Alzheimer's is said to be the most common and most researched type of dementia.
Up to a third of Alzheimer's in elderly people may instead be LATE, says the international team of researchers. LATE usually affects people over 80 years old according to the study. The work analysed evidence from thousands of post-mortem results.
There's no doubt that many people who were previously called Alzheimer's, in fact, did not have Alzheimer's.", lead author Dr Pete Nelson, from the University of Kentucky, said.
Trials of drugs to reduce proteins in the brain that were thought to cause Alzheimer's have failed. There have been no effective new treatments. Having a better understanding of LATE might lead to the discovery of new treatments, say the researchers.
They have written guidelines to help increase awareness and advance research into the newly defined disease.
This is probably the most important paper to be published in the field of dementia in the last five years, Prof Robert Howard from University College London said.