22    Immunocompromise

The availability and efficacy of highly active antiretroviral treatment has rendered the CNS manifestations of HIV—HIV encephalopathy, progressive multifocal leukoencephalopathy (PML), and toxoplasmosis—somewhat less common. The recognition of these entities on MRI is nevertheless important, HIV encephalopathy being the most frequent. The mechanism of this condition involves the direct viral infiltration of neurons, which correlates with diffuse hyperintensity of the cortical gray matter and subcortical white matter on T2WI. Eventually these changes may involve the periventricular white (Figs. 22.1A,B) and deep gray matter. Such lesions are typically isointense brain to parenchyma on T1WI (Fig. 22.1.C) and rarely enhance. With treatment, initial worsening of the lesions is seen on MRI, and although white matter disease usually resolves, central and peripheral cortical atrophy often persists. Such atrophy is in fact the most common MRI finding in HIV encephalopathy, demonstrated in Fig. 22.1C along with the loss of gray–white matter differentiation, another common finding. DWI and DTI (diffusion tensor imaging) changes may precede those of conventional MRI, and spectroscopic findings include a decrease in NAA (from neuronal loss), an increase in choline (from membrane turnover), and increased myoinositol (a marker for neuroglial activation).

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