PML

· World-wides cases in the order of 350 in early 2013.

· The clinical and imaging pattern of natalizumab cases is different to that which was observed with AIDS

· Several cases are have been identified in asymptomatic patients

Survival

· Unilobar 85%

· Widespread 66%

Imaging Findings

Location

· Unilobar more common than multifocal

· More often subcortical/juxta-cortical than periventricular

· Has never been observed in the spinal cord

Specific Lobes:

o Frontal lobe 45% - most common

o Occipital 20%

o Parietal 12%

o Temporal 10%

o Cerebellar 10%

o Thalamus – rare cases (small ‘stroke-like’ lesions)

MRI

· Increased T2 – can have a ground glass, microcystic appearance

· FLAIR – most obvious on FLAIR, given it is often juxta-cortical the signal can be confused with CSF on T2

· Decreased T1 – can have a ‘moth-eaten’ appearance

· +/- Contrast enhancement (present in 35%)

· DWI – increased signal (but not as bright as an acute infarct). Area of DWI change often larger in extent than area of FLAIR signal

· Other features

o Cortical thickening

o A cortical ribboning

o Punctate clusters of T2 lesions

Progression

· In retrospect looking back at MRI’s done prior to the diagnostic one there is often some evidence of the lesion for about 4 months prior.

· Progression of the lesion over months is a key difference from demyelinating lesions.

Diagnosis

CSF

· JC virus PCR

o specific for pathological PML

o 76% sensitive

· Non-specific WCC usually less than 20

· Moderate elevation of protein