Cognitive impairment in people with AIDS exists in two forms - one mild, another severe - each affecting different areas of the brain, according to the results of a University of Pittsburgh School of Medicine study presented at the American Academy of Neurology 58th Annual Meeting in San Diego, Calif.
The researchers say their findings indicate there probably are two separate mechanisms that can cause cognitive impairment in people with AIDS.
"The advent of combination antiretroviral therapies to treat AIDS has significantly changed the course of the disease," said James T. Becker, Ph.D., professor of psychiatry, neurology and psychology at the University of Pittsburgh. "Not only are people living longer with AIDS, but we are finding that a number of the other co-existing conditions that people with AIDS often experience are becoming less severe. Such is the case with cognitive impairment - we are finding less people have severe cases while more have milder forms."
Cognitive impairment in people with AIDS is caused when the HIV virus attacks the brain and can be a complicated syndrome resulting in deficits in mood, behavior, motor coordination and thought processes. Studies have shown that, especially since the advent of the first combination antiretroviral therapies, the incidence of severe dementia in people with AIDS has decreased significantly. However, AIDS-related dementia isn't disappearing, and a greater number of people are living with a milder form of cognitive impairment.
The study evaluated 54 participants with AIDS and 23 HIV-negative control subjects. Participants completed a detailed neurobehavioral evaluation, which included neuropsychological testing to assess what level of cognitive impairment they had, and underwent an anatomical MRI scan. Using the data from the neurological tests, each participant was classified as either normal, mildly impaired or severely impaired. The MRI data were analyzed separately using voxel-based morphometry, a technique that allows researchers to analyze the entire brain and identify areas where tissue has atrophied.
Of the 54 participants with AIDS, 17 demonstrated some level of mental impairment. The mild impairment group only showed problems in the area of psychomotor speed, which is a measure of the time it takes a person to receive a signal, process it and respond. Based on the MRI scans, this group demonstrated atrophy in the frontal and anterior cingulate cortices, areas of the brain that control many vital functions, including memory, emotion and stimulus response.
Those in the severe impairment group showed impairments in psychomotor speed as well as in memory and visual-spatial processing. This group had more significant atrophy that was located in the caudate and putamen, different areas than the mild group. The caudate and putamen also have some of the highest levels of HIV found in the brain. The caudate and putamen are part of a circuit between the cortex and other areas of the brain, and are especially vulnerable to HIV infection.
"The next step is to find out what the mechanisms are behind these two patterns of cognitive function. Once we gain a better understanding of what causes the mental impairment and how it is caused, we can begin to look into new ways to treat or even prevent the symptoms," added Dr. Becker.