Hiv encephalitis

A syndrome characterized by a slowly progressive impairment of fine motor control, verbal fluency and short-term memory followed after a few months by severe deterioration and subcortical dementia with a near vegetative state as a possible final stage. This syndrome (ADC - AIDS dementia complex) affects from 33 to 67% of AIDS patients and is the most frequent neurological manifestation of HIV infection. For a general description of the disease, see acquired immunodeficiency syndrome AIDS .

Neuroradiological correlates are brain atrophy easily depicted by both CT and MRI. Characteristic parenchymal changes often missed by CT scan are also present. On MRI they appear as a fluffy, nonfocal signal hyperintensity on T2-weighted images involving bilaterally the periventricular and centrum semiovale white matter. The distribution and existence of such lesions does not necessarily correlate with the clinical picture and a certain degree of parenchymal involvement may be visible in asymptomatic patients. However extensive white matter involvement is more likely to be symptomatic. Contrast enhancement is usually absent.

Pathological correlates to these findings are reactive gliosis, focal necrosis and demyelination associated with only mild neuronal loss, and minor inflammatory changes consisting of perivascular macrophage infiltrates and microglial nodules.

MR spectroscopy depicts reductions in N-acetyl aspartate consistent with neuronal loss and increased levels of choline in white matter reflecting astrocytosis or microglial proliferation. The pattern of conventional MR changes in HIV encephalitis is nonspecific compared to other forms of viral encephalitis such as CMV (initially thought to be the aetiological agent of ADC). Infection by other viruses not infrequently coexist. The differential diagnosis also includes PML: as compared to PML, HIV encephalitis has a more homogeneous and diffuse aspect and characteristically it does not involve the subcortical U-fibres. Studies of magnetization transfer ratio by MR have also been applied with success in this differential diagnosis as PML lesions show a dramatic decrease in MTR as compared to lesions in HIV encephalitis.

FS