A new University of California - Los Angeles/University of Pittsburgh imaging study for the first time shows the selective pattern of destruction inflicted by AIDS on brain regions that control motor, language and sensory functions. High-resolution 3-D color scans created from magnetic resonance images (MRI) vividly illustrate the damage.
Published Oct. 10 by the online Proceedings of the National Academy of Sciences, the research offers a new way to measure the impact of AIDS on the living brain, and reveals that the brain is still vulnerable to infection when patients are receiving highly active antiretroviral therapy (HAART).
"Two big surprises came out of this study," explained Paul Thompson, Ph.D., first author and associate professor of neurology at the David Geffen School of Medicine at UCLA. "First, that AIDS is selective in how it attacks the brain. Second, drug therapy does not appear to slow the damage. The brain provides a sanctuary for HIV where most drugs cannot follow."
Thompson's laboratory used a new 3-D brain-mapping technique developed at UCLA to analyze the MRIs of 26 people diagnosed with AIDS, and then compared the scans to those of 14 HIV-negative people. The brain scans measured the thickness of gray matter in various regions of the cerebral cortex.
The University of Pittsburgh diagnosed and scanned the AIDS patients; all 26 subjects had lost at least half of their T-cells, the immune cells targeted by HIV. None had experienced AIDS-related dementia, and 13 were on HAART.
The striking differences between the AIDS patients' and the control subjects' brain scans were easy to see on the detailed 3-D images. Areas of tissue loss glowed red and yellow, while intact regions shone blue and green.
The researchers were surprised to discover that AIDS consistently injured the brain's motor, language and judgment centers, but left other areas alone. Specific patterns of tissue damage directly correlated with patients' physical and mental symptoms, including impaired motor coordination and slowed reflexes.
"The brain scan really catches AIDS red-handed, allowing us to see precisely where the damage is," Thompson observed. "For the first time, we can understand why motor skills deteriorate with AIDS, because the virus attacks the motor centers on top of the brain."
"We saw up to a 15-percent tissue loss in the brain centers that regulate motor skills, such as movement and coordination," added Thompson. "This helps explain the slowed reflexes and disruption of balance and gait that often affect people with early AIDS."
The UCLA team also linked thinning of the language cortex and reasoning center to depletion of T-cells from the immune system. The finding may shed light on why AIDS is often accompanied by mild vocabulary loss, judgment problems and difficulty planning. As the disease advances, these symptoms can worsen into memory loss and dementia similar to Alzheimer's disease.
"Tissue loss follows T-cell loss, meaning that people with poor immune function also show severe brain damage," explained Thompson. "This was a revelation. We used to consider these separate phenomena, because HIV harms the brain and immune system in different ways. Now we see they are intrinsically linked."