Progressive Multifocal Leukoencephalopathy (PML)

A 30 yo male, known HIV Positive, present with right side weakness. 

Findings:
Multiple patchy T2 white matter hyperintensities in cerebral white matter in fronto parietal region, basal ganglia, thalami as well as corpus callosum,
Bilateral asymmetrical involvement,
Non enhancing on post contrast T1.
Faint bright signal on diffusion attributed to prolonged T2 effect.
No mass effect.
Mild diffuse cerebral cortical atrophy.

Imaging diagnosis : Progressive Multifocal Leukoencephalopathy (PML)

PML

A sub acute progressive demyelinating disease.
Bad prognosis, even fatal.
Seen in patients with immune disorders particularly impaired cell mediated immune response. Predominantly occurs in patients with AIDS, in ~ 5% of patients with AIDS. Results from JC virus infection - genus Polyomavirus -  family Papovaviridae. Before AIDS epidemic, PML was rare and was associated with other immune compromised conditions like leukemia, lymphoma, organ transplantation and severe combined immunodeficiency (SCID).

Imaging findings:

MRI is the preferred imaging modality over CT.
Usually bilateral and asymmetrical involvement. Patchy and multifocal. Unilateral involvement uncommon.
Predominantly involve fronto parietal white matter; may involve periventricular white matte or sub cortical white matter or both.
On CT, ill defined patcy areas of low attenuation. No enhancement on post contrast.
On MR, ill defined patchy areas of T2 hyperintensity. May show high signal on diffusion due to prolonged T2 effect. No enhancement on post contrast T1.

An associated atrophy,  increase in confluence of lesions, increase in hypo intensity of lesion on T1,  involvement of corpus callosum are poor prognostic indicators.

Faint enhancement seen on post contrast T1 in follow up MRI of PML pts treated with Anti Retroviral Therapy is associated with increase in their CD4+ count, may indicate favourable prognosis.

DD:
HIV Encephalitis / Leukoencephalopathy : Usually characterised by bilateral symmetrical Periventricular T2 white matter hyperintensity, an associated diffuse cortical atrophy and ventricular dilatation which are not predominant findings of PML. Clinically PML is associated progressive focal motor and sensory deficits, whereas HIV leukoencephalopathy pt present with altered cognition.

Case of Hiv-encephalitis-encephalopathy
Hiv-encephalitis-vs- PML