HIV and the brain: functional investigations in drug users

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Abstract
The investigation of the effects of HIV infection in drug users has had a low priority in most centres. The unusual circumstances in Edinburgh, where epidemic infection of drug users occurred in 1983-84, have provided the opportunity for clinical investigation of the consequences of brain involvement by HIV employing neurophysiological, neuropsychological and brain imaging techniques. Averaged evoked potential studies have shown abnormalities in both the amplitude and latency of the P300 response to unexpected tones in both seropositive and seronegative drug users compared with normal controls. However, illness progression to or within CDC stage IV is associated with lengthening of the P300 latency which suggests impairment of information processing speed. The results of neuropsychological testing similarly show important impairment of cognitive function in most domains in all drug users, irrespective of the stage of HIV disease. This means that the assessment of individual drug users can only be made in relation to the normal values for the drug-using population. This normal range for a variety of tests is presented. However, as with the neurophysiology, further impairment occurs on retesting patients with stage IV disease. This apparent effect of illness progression is most marked in tests of memory and information processing speed; it is not influenced by subjective ratings of mood. Thus, tests of brain function can only detect the effects of illness in stage IV or symptomatic patients. Preliminary studies employing quantitative magnetic resonance imaging suggest the potential for measuring brain involvement before functional impairment is evident. The problems of detecting minor cognitive impairment rather than dementia in drug users are discussed.