Neurological complications afflict the majority of people who are infected with HIV. These include opportunistic infections, tumours, vascular and metabolic complications, and also disorders that are unique to AIDS itself and associated with infection of the nervous system by HIV [1]. Although the use of different antimicrobial treatments has led to a significant increase in the survival of AIDS patients, many of the nervous system disorders still represent a diagnostic and therapeutic challenge.

The clinical diagnosis of central nervous system (CNS) diseases in patients with AIDS is based on neurological examination and neuroimaging studies. Further examinations, such as standard analysis of cerebrospinal fluid (CSF), electroencephalography and neuropsychological assessments, may also be useful. None of these investigations, however, provides specific information, and only the identification of a pathogen in the CSF or brain makes a diagnosis of aetiology possible. In some cases, conventional microbiological techniques applied to analyse CSF, such as the isolation of bacteria, mycobacteria and fungi, and the detection of Cryptococcus neoformans polysaccharide antigen, are adequate for diagnosis. CSF examination may also be helpful in demonstrating the presence of tumour cells in cases of metastatic CNS lymphoma, or in revealing Venereal Disease Research Laboratory (VDRL) test reactivity in cases of neurosyphilis, but these conditions represent only a minority of CNS complications. On the other hand, brain biopsy is indicated in limited instances, although this is often impracticable because of the critical condition of the patients. CNS diseases in AIDS patients are therefore often diagnosed on clinical grounds, by either excluding other conditions or evaluating the response to specific treatments. A definitive aetiological diagnosis can frequently only be established at post-mortem examination.