Retroviruses

• i. Large group of RNA viruses that use reverse transcriptase which allows viral RNA to be utilized as a template to make DNA; infects T4 bearing cells but even uninfected T4 cells do not function normally
• ii. Two main groups
  • 1. lentiviruses – including HIV
    • a. AIDS dementia complex
      • i. In later stages of HIV infection, the commonest neurologic complication is a subacute or chronic HIV encephalitis presenting as a form of dementia (AIDS dementia complex – incidence is 15% over patient’s life)
      • ii. Histopathology: diffuse and multifocal rarefaction of the cerebral white matter accompanied by scanty perivascular infiltrates of lymphocytes and clusters of foamy macrophages and multinucleated cells
      • iii. Commonly associated with myelopathy
    • b. Myelopathy, peripheral neuropathy and myopathy
      • i. Vacuolar degeneration similar to subacute combined degeneration is associated with AIDS dementia complex
      • ii. AIDS patients may also have various forms of peripheral neuropathy, predominantly symmetrical sensory and dysesthetic in about 40% of patients; sensory symptoms and pain predominate
      • iii. May also get inflammatory polymyositis during any stage of the disease
      • iv. Zidovudine (used to treat HIV infection) may produce a myopathy; AIDS patients also have a high rate of alcohol, cocaine and heroin use which may also cause a myopathy
    • c. Opportunistic infections and neoplasms of the CNS in AIDS
      • i. Cerebral toxoplasmosis is the most frequent focal complication (13% of autopsy patients) followed by primary CNS lymphoma (5% of autopsy patients), progressive multifocal leukoencephalopathy and focal encephalitis
      • ii. Most frequent nonfocal complication of AIDS is CMV and crytpococcal infections; CMV is present in 15% of AIDS autopsies and typically occurs in advanced HIV disease with CD4 counts under 100; CNS CMV diagnosis is usually done by diagnosing CMV infection elsewhere in the body; CMV infection in the CNS is usually associated with negative viral cultures
  • 2. oncornaviruses – including the human T-cell leukemias and lymphomas