According to a recent research, published in the journal Brain, millions of elderly people have a form of dementia that has been misdiagnosed as Alzheimer’s disease.

One expert called it the most important dementia finding in years.

The condition, limbic-predominant age-related TDP-43 encephalopathy, or Late, shares similar symptoms to Alzheimer’s, but it is a distinct disease.

The new discovery may partly explain why finding a dementia cure has failed so far.

Dementia is not a single disease, but is the name for a group of symptoms that include problems with memory and thinking.

There are lots of different types of dementia and Alzheimer’s is said to be the most common and most researched.

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However, up to a third of Alzheimer’s in elderly people may instead be Late, says the international team of researchers, although both dementias can co-exist.

The newly discovered dementia appears to affect the “oldest old” – people over 80 – according to the work that looked at evidence from thousands of post-mortem results.

One in five in this age group has it, meaning the public health impact of the disease will be large, say the researchers.

Unlike Alzheimer’s, Late tends to cause a more gradual decline in memory, they believe.

Currently, there is no specific single test for dementia.

Signs of it can sometimes be seen in the brain after death.

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.

Scientists have been striving to find a cure for dementia, but with so many different types and causes of the disease, the goal has proved difficult.

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 and some pharmaceutical companies have dropped out of the dementia drug race.

According to researchers, having a better understanding of Late might lead to the discovery of new treatments.