The shifting patterns of HIV encephalitis neuropathology.
HIV infected macrophages infiltrate the nervous system early in the progression of HIV infection, leading to a complex set of neuropathological alterations including HIV encephalitis (HIVE), leukoencephalopathy and vacuolar myelopathy that in turn result in neurodegeneration of selective cellular populations and pathways involved in regulating cognitive and motor functioning. Rapid progress in the development of highly active antiretroviral therapy (HAART) has changed the patterns of HIV related neuropathology and neurological manifestations in the past 10 years. The prevalence of opportunistic infections and central nervous system (CNS) neoplasms has decreased, and some groups have proposed that the frequency of chronic forms of HIVE have been rising as the HAART-treated HIV population ages. Accordingly, clinical manifestations have shifted from severe dementia forms to more subtle minor cognitive impairment, leading to the suggestion of a classification of HIV associated neurological conditions into an inactive form, a chronic variety, and a 'transformed' variant. From a neuropathological point of view these variants might correspond to: a) aggressive forms with severe HIVE and white matter injury, b) extensive perivascular lymphocytic infiltration, c) 'burnt-out' forms of HIVE and d) aging-associated amyloid accumulation with Alzheimer's-like neuropathology. Factors contributing to the emergence of these variants of HIVE include the development of viral resistance, immune reconstitution, anti-retroviral drug toxicity and co-morbid factors (e.g., methamphetamine, HCV). More detailed characterization of these proposed variants of HIVE is important in order to better understand the pathogenesis of HIV-associated neurological damage and to design more effective treatments to protect the nervous system.