The definition of HIV-specific neuropathology.

Evaluation of a neuropathological series of 160 HIV-infected patients, almost all in the terminal AIDS stage of the infection, allowed recognition of novel syndromes which can be regarded as HIV-specific neuropathology because: 1) they are not observed in non-HIV tissues; 2) HIV is, in our hands consistently by immunocytochemistry, demonstrable in large amounts within these lesions; 3) other pathogens are not detectable within these lesions; and 4) these lesions may occur in isolated fashion within CNS tissues (40% of HIV-specific neuropathology in this series), without any other CNS pathology. HIV-specific neuropathology was found in 34% in this series and comprised two prototypes within a spectrum of frequently overlapping changes: multifocal microgranulomatous lesions of HIV encephalitis, and diffuse white matter damage of HIV leukoencephalopathy. In almost all cases, multinucleated giant cells signal the local presence of HIV in routine stains. In contrast to HIV-specific neuropathology, various unspecific nervous tissue syndromes do not consistently exhibit the local presence of HIV and thus are designated HIV-associated or possibly HIV-induced lesions: lymphocytic meningitis, vacuolar myelopathy, multifocal vacuolar leukoencephalopathy, and diffuse poliodystrophy. Although these unspecific syndromes may also contribute to clinical manifestations, their pathogenetic relation with HIV remains to be established.