Diagnosing early alzheimer's requires distinguishing symptoms from those of normal aging.

Scientists from the Karolinska Insitute in Sweden crunched data from 47 studies involving 1,207 people who developed Alzheimer's and 9,097 others who stayed healthy.

They identified a number of telltale pre-clinical problems that predicted later Alzheimer's.

Warning Signs

These include declines in general mental ability, episodic memory, perceptual speed and executive functioning (the brain's ability to absorb information).

Smaller deficits were seen in verbal ability, visuo-spatial skill and attention.

Similar Symptoms

However, the findings, published in the journal Neuropsychology, present experts with a problem.

Many of the symptoms mirror those seen in normal aging, only they are more pronounced. Making a reliable early diagnosis of Alzheimer's will require being able to spot the differences accurately.

Onset Precedes Diagnosis

The data also confirmed previous findings that Alzheimer's develops with a period of early onset followed by relative stability until a few years before diagnosis.

At this point, the patient's condition plummets.

The study found that preclinical impairment was greatest when the disease started young and progressed quickly.