HIV Encephalitis

      A subacute encephalitis involving the white matter is seen in up to 30% of patients with AIDS related to direct invasion of neurons by the neurotropic retrovirus, human immunodeficiency virus type 1 (HIV). Presenting symptoms include headache, memory loss, language difficulty, movement disorders, and various sensory deficits. More advanced disease is signaled by behavioral disorders, loss of bowel and bladder control, and the AIDS dementia complex. HIV and cytomegalovirus often coexist in brain specimens taken from patients with AIDS; however, HIV seems to be the predominant etiology for the microglial nodules and multinucleate giant cells, the pathologic hallmarks of the white matter encephalitis. ^,

      The MR picture is one of bilateral, diffuse, patchy to confluent areas of increased signal intensity on T₂-weighted images with poorly defined margins involving the white matter of the cerebrum, cerebellum and brain stem. The white matter changes are not as striking as in many other demyelinating diseases. Initially, the images may show only a hazy mottled pattern of hyperintensity within the centrum semiovale. HIV encephalitis does not enhance with gadolinium. The MR appearance is distinct from that of PML, and the clinical setting readily separates it from other white matter abnormalities. As with PML, the white matter abnormality on MRI often improves or remains stable after therapy with protease inhibitors, correlating with clinical improvement.

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