Neurologists who study AIDS have watched, waited and worried for nearly a decade about the long-term effect of HIV on the brain. They've known that the drug cocktails that so effectively extend lives don't protect the brain very well from the virus.
Now they've gotten their first actual look at the destruction HIV causes in living brains. A study published by the National Academy of Sciences last month used 3-D brain scans to see how much tissue was damaged. In vivid, color-coded images, researchers found up to 15% tissue loss in the centers that regulate movement and coordination, as well as a thinning of the language and reasoning centers.
"As people are living longer, the major risk of HIV is not the immune system anymore, but the brain," said Dr. Paul Thompson, professor of neurology at the UCLA School of Medicine and author of the brain scan study. "People who are doing well with HIV, living with it for over 10 years, have this progressive damage going on in the brain, well before symptoms are obvious."
For the more than 1 million Americans living with HIV, the virus that causes AIDS, it could mean minor problems with forgetfulness -- or it could mean early-onset dementia is on the horizon.
The study compared 26 infected people on treatment -- none of whom showed symptoms of dementia -- with 14 HIV-negative people. The brain deterioration seen among those with AIDS could cause slowed reflexes, mild vocabulary loss or poor judgment.
There just isn't enough experience with the multi-drug treatment, available only since 1996, to predict whether symptoms will stabilize or worsen.
It's long been understood that the drugs that keep HIV in check, like many other medicines, don't get to the brain in the same way they get to other organs. That's because blood vessels in the brain are less permeable than those elsewhere in the body and have an additional coating to prevent blood leakage into brain cells.
"It's as though you have a tight pipe, and then insulate it more," said Dr. David Clifford, head of the Neurologic AIDS Research Consortium at Washington University School of Medicine in St. Louis. The biological design, called the blood-brain barrier, is nature's way of protecting the brain. But it also acts to make it more difficult, though not impossible, for helpful drugs to get in. The brain ends up being a sort of sanctuary for HIV.
