This is a continuation of our previous studies on Progressive Multifocal Leukoencephalopathy (PML). We will focus on the role of inflammation in PML, and define prognostic markers of disease evolution.

To determine precisely what are the host or viral factors that may predict a favorable outcome for PML patients and the role of inflammation in preventing JCV from causing brain disease. One of the goals of this study is to help establish non-invasive markers of PML evolution by studying the brain metabolism in PML lesions using Magnetic Resonance Imaging (MRI), Magnetic Spectroscopy (MRS) and other advanced imaging modalities.

Inclusion Criteria:

• PML patients of 18 years of age or older will be included in this study.

Exclusion Criteria:

1. Presence of opportunistic brain lesions other than PML. ( e.g., toxoplasmosis, lymphoma)
2. Presence of confounding neurological disorder such as brain neoplasm etc.

In addition patients with a contraindication to MRI examination will be excluded from study. Contraindications to the MRI examination include:

1. Medically unstable or hematological, renal, or hepatic dysfunction.
2. Cardiac pacemaker
3. Internal clips,
4. Metal implants, or external clips with 10 mm of the head.
5. Metal in the eyes.
6. Pregnant
7. Claustrophobia

PML patients of 18 years of age or older in the Boston area will be included in this study.

The control groups will include HIV+ and HIV- individuals who need to have a lumbar puncture for their clinical management.