One of the major problems encountered when attempting to diagnose and treat HIV positive patients is determining the extent to which the virus has affected the brain. The technique of magnetic resonance spectroscopy (MRS) is ideally suited to the examination of this problem. MRS focuses on using magnetic resonance to explore the chemical composition of given regions. The two brain chemicals of particular interest for these MRS studies are N-acetyl aspartate (NAA) peak and myo-inositol (ml). The level of NAA is used as an index of neuronal integrity, and since neurons are primarily located in the gray matter of the brain, changes in the level of NAA can provide some indication of viral-induced neuronal damage. Alternatively, mI may be used as an index of glial damage, and since the density of glia is highest in the white matter of the brain, mI can be employed to monitor viral induced damage to glia. The MRS studies showed that there are biochemical differences between uninfected normal controls, HIV patients that are symptomatic and those that are asymptomatic. The patients who were symptomatic (diagnosed with ADC) had decreased levels of NAA in gray matter when compared to both normals and asymptomatic patients. In contrast, patients who were asymptomatic (no clinical evidence of ADC) had increased levels of mI in white matter. These results suggest that the evaluation of the gray matter and white matter in the frontal lobe of the brain by high resolution MRS will identify early changes in brain metabolism that precede the damage of neurons, helping to select patients for possible therapies before irreversible damage may occur. Additionally, this MRS approach may be a good method to objectively evaluate the degree and progression of ADC and to monitor the effect of therapy. This high resolution MRS approach, which gives a precise and sequential evaluation of metabolic alterations in gray and white matter, will contribute to the understanding of the pathophysiology of this disorder.
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