What is the most likely diagnosis for a patient with AIDS exhibiting progressive memory loss and an MRI showing diffuse, bilateral hyperintensities in the white matter?

The diagnosis of HIV encephalopathy is supported by the presentation of progressive memory loss in a patient with AIDS, especially when paired with MRI findings of diffuse, bilateral hyperintensities in the white matter. HIV encephalopathy is characterized by cognitive impairment, which can manifest as memory loss, confusion, and behavioral changes.

The MRI findings highlight the impact of the HIV virus on the brain, leading to neuronal damage, which often presents as increased signal intensity in the white matter due to edema or other pathological changes. This involvement of the white matter is a distinguishing feature that aligns well with HIV-related neurological complications.

In contrast, other conditions listed, such as cryptococcal infections or Pneumocystis jirovecii infection, do not typically present with these specific MRI findings or this pattern of progressive cognitive decline. Lymphoma may cause lesions on imaging but often presents as focal masses or enhancing lesions, which differs from the diffuse changes seen in HIV encephalopathy. Therefore, the overall clinical picture and imaging results point clearly towards HIV encephalopathy as the most likely diagnosis.