Tests for Alzheimer's disease?

According to this article in the New York Times, a test of spinal fluid that looks for certain markers of Alzheimer's disease may be able to aid an early diagnosis in people with memory loss.

Alzheimer’s, medical experts now agree, starts a decade or more before people have symptoms. And by the time there are symptoms, it may be too late to save the brain. So the hope is to find good ways to identify people who are getting the disease, and use those people as subjects in studies to see how long it takes for symptoms to occur and in studies of drugs that may slow or stop the disease.

However, the article goes on to raise the question: since we don't have any reliable treatment for the disease, what's the point of undergoing a possibly painful or at least uncomfortable test to confirm that you've got it?

Thanks to Derek Colanduno of Skepticality for directing my attention to this article.