6-BILLION NEURONS LOST IN AIDS - A STEREOLOGICAL STUDY OF THE NEOCORTEX

Human immunodeficiency virus type 1 (HIV1) is neurotropic. One of the morphological changes that is seen in patients with acquired immunodef iciency syndrome (AIDS) is cerebral atrophy affecting various structur es including the neocortex. The cause of atrophy is not known. The tot al number of neocortical neurons was estimated in formalin fixed brain s of 12 males with AIDS and 12 male controls matched for age and heigh t. The mean number of neocortical neurons was 16.0X10(9) (coefficient of variation=0.11) in the AIDS patients compared with 21.9X10(9) (coef ficient of variation=0.22) in the controls, a difference of approximat ely six billion (p<0.005, 2-tailed). The global neuronal loss was 37%, and affected all four neocortical lobes. Ten patients did not have a history of central nervous system symptoms; two patients had a history of dementia. The number of neurons in the AIDS cases was not associat ed with dementia. AIDS is the first disease in which a global loss of neocortical neurons has been demonstrated using unbiased stereological methods. The loss of more than one third of the neurons may partly ex plain the cortical atrophy. Focal neuron loss has been reported by sev eral authors, but none have been based on unbiased methods. In this gr oup of AIDS patients the severe loss of neurons did not correspond to neurological deficits.