Progressive multifocal leucoencephalopathy (PML) is an opportunistic infection caused by JC virus (JCV) in immunodeficient individuals. The pathological hallmark is irreversible white matter demyelination. The diagnosis is supported by the clinical presentation (subacute motor deficits, ataxia and cortical visual symptoms), characteristic findings on magnetic resonance imaging (MRI) of the brain (bilateral, asymmetric, well-demarcated, T2 hyperintense white matter lesions with no oedema) and JCV detection by polymerase chain reaction (PCR) in the cerebrospinal fluid (CSF).
We obtained retrospective data for all JCV PCR test results performed on CSF samples between March 2002 and November 2011 from HIV-seropositive patients at Chelsea & Westminster Hospital NHS Trust. In total, 564 CSF samples from HIV-positive patients were tested for JCV during 117 months, of which seven (1.24%) were positive. Contemporaneous MRI imaging of the brain was performed in 360 of 564 patients (63.8%) (Table 1).
|Contemporaneous MRI of the brain report||Number of CSF samples tested for JCV||Number of positive JCV tests||Percentage of positive samples|
|Suggestive of PML||64||3||4.69|
|Suggestive of an infectious, but non-PML, pathology||77||2||2.60|
|Normal or suggestive of a noninfectious pathology||219||1||0.46|
|MRI not performed||204||1||0.49|
The gold standard for diagnosis of PML is brain biopsy. However, this is often unsafe, unethical or unnecessary. The combination of an appropriate clinical presentation and typical findings on brain MRI is often sufficient to make the diagnosis, for which highly active antiretroviral therapy (HAART) is the evidence-based treatment. The utility of JCV PCR testing in the CSF of HIV-seropositive individuals is under question (sensitivity for MRI-proven PML = 24–89.5% [2, 3]). Unsurprisingly, the use of HAART has been shown to reduce the sensitivity of this test (57.5% vs. 89.5% in patients not on HAART ).
JCV was infrequently detected in the CSF of HIV-positive individuals over a 9-year period. Although JCV was more frequently found in the CSF of patients with MRI findings suggestive of PML, the detection rate was still <5%, suggesting a very high false negative rate for this test. CSF JCV testing should not be performed routinely when MRI of the brain is normal or suggestive of a noninfectious pathology. Even when PML is suspected on MRI of the brain, JCV CSF is unlikely to be positive. We conclude that many of these tests are unnecessary, offering a potential to significantly reduce costs without compromising patient care.