The Edinburgh cohort of HIV-positive drug users: current intellectual function is impaired, but not due to early AIDS dementia complex.

Eighty people, all infected by HIV-contaminated drug injection equipment between 1983 and 1984, completed the National Adult Reading Test (NART) and selected revised Wechsler Adult Intelligence Scale (WAIS-R) subtests. Demographic variables (age, sex, years of education, and social class) were recorded as additional indices of premorbid functioning. Cross-sectional comparison of NART and WAIS-R scores showed that cognitive function was not more impaired with increasing severity of HIV illness, as defined by clinical staging. Nor were HIV-positive patients more impaired than a control group of seronegative drug users. Mean NART scores did not differ significantly from that predicted by a regression model, indicating that the NART can be reliably used to estimate premorbid intelligence for this population. However, current performance on WAIS-R subtests was below that expected from population models of cognitive function that combine measures of premorbid IQ and demographic factors, providing evidence of impaired intellectual function. Currently observed cognitive deficits are probably more due to drug use than to the insidious onset of AIDS dementia complex.