The advent of HIV radically

changed the epidemiology from what was an exceptionally rare complication of patients with reticuloendothelial disease or immunosuppressed following organ transplantation, to an OI identified in up to 5% of patients with AIDS with limited reduction after introduction of HAART and no change in the high mortality rate [98,99]. PML caused approximately 20% of focal brain lesions pre-HAART [100]. The cardinal pathological feature and underlying process determining the clinical presentation is demyelination of white matter, which is irreversible. Classic PML Bioactive Compound Library molecular weight presents as a subacute illness without constitutional symptoms in patients with severe immunodeficiency. Progressive focal neurology, mainly motor deficit, altered mental

or mood status, ataxia or cortical visual symptoms, develop over weeks to months. The presence of the focal features helps distinguish the cognitive syndrome associated with PML from HIV encephalopathy. Seizures may rarely occur. Rare but increasingly recognized PML may present after the introduction of ARV treatment and reflects an immune reconstitution phenomenon [101]. MRI appearances and JC virus detection by PCR in a CSF sample are sufficient to make a diagnosis in most cases and avoid the need for a brain biopsy (level III recommendation). Early diagnosis is paramount. Brain biopsy has long been regarded as the gold IWR-1 research buy standard with a sensitivity of 64–96% and a specificity of 100%. With imaging refinements, MRI combined with CSF DNA amplification has allowed avoidance of biopsy. Lesions are usually bilateral, asymmetric, non-enhancing T2 hyperintense T1 hypointense, restricted to white matter and with no oedema. The asymmetric nature and sharp demarcation helps differentiate from HIV encephalopathy. In the context of antiretroviral treatment, features may be atypical. Pre-HAART, PIK3C2G JC DNA in the CSF detected by PCR had sensitivity of 72–92%

and a specificity of 92–100%. However, since the introduction of HAART sensitivity has fallen to approximately 50% reflecting reduced viral replication and increased clearance of virus from the CSF [102,103]. Factors associated with a poor prognosis include clinical (older age, brainstem involvement, lowered level of consciousness), viral (high CSF JC viral load with delayed clearance with HAART), radiological (early brainstem involvement), and immunological (CD4 count <100 cells/μL) [104]. Evidence of immunological responsiveness, higher CD4 cell counts, contrast enhancement on imaging, perivascular mononuclear infiltrates and JC-specific cytotoxic T lymphocytes are associated with improved prognosis. HAART is the only intervention that has improved clinical outcomes with PML (category III recommendation).