Original articleUse of quantitative susceptibility mapping (QSM) in progressive multifocal leukoencephalopathy
Introduction
Progressive multifocal leukoencephalopathy (PML) is a rare demyelinating disease of the central nervous system that results from reactivation of latent JC virus (JCV). This opportunistic encephalopathy was first described in patients with Hodgkin's lymphoma, chronic lymphocytic leukemia and then in patients with AIDS. In the past few years, other conditions have been associated with PML, including treatment with monoclonal antibodies such as natalizumab for multiple sclerosis [1]. In this situation, the incidence of PML is 11.1 per 1000 in JCV antibody-positive patients with a prior use of immunosuppressant and a treatment duration exceeding 24 months [1].
PML was previously considered as a fatal disease. It has been recently demonstrated that an early PML diagnosis is associated with a favorable prognosis, in certain conditions such as natalizumab therapy [2], [3]. Thus, improving diagnostic tools should allow early diagnosis of PML with good specificity.
Brain MRI has been included in PML diagnostic criteria, because of its high sensitivity in the screening of PML, even before the onset of clinical symptoms [4]. Despite this high sensitivity, it has been demonstrated that MRI findings are heterogeneous, especially in the early stages of PML.
Susceptibility-weighted imaging (SWI) low signal intensities in U-fibers adjacent to the white matter lesions of PML have been recently described [5]. Besides, we recently reported the use of quantitative susceptibility mapping (QSM) in a patient with PML whose MRI revealed hypointensities in the cortex adjacent to white matter abnormalities, in T2-weighted gradient echo (T2 GRE) sequence and SWI [6]. Currently, the significance of these hypointensities remains unknown.
Section snippets
Population
This prospective study was conducted between September 2014 and February 2015. Inclusion criteria were:
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a history of PML with a definite diagnosis according to the official AAN Neuroinfectious Disease section criteria [4]. In particular, positive PCR detection of JCV DNA in the CSF of all patients;
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agreement to undergo a new MRI examination.
Four patients were included as well as 4 control subjects.
Ethical approval
The institutional review board of the University Hospital Center of Montpellier gave its approval
Results
Four patients were included, all men. The mean age at the MRI was 47 years (range: 41–55). The mean PML duration at the time of MRI was 24.2 months (range: 5–67). Reference ratios recorded in volunteers were between −0.01312 and 0.02795.
Discussion
PML characteristics on conventional brain MRI are well known: single or multiple hyperintense areas in T2-weighted images, which become confluent and large with disease progression [8]. Classically, there is no mass effect and the borders of the lesions are irregular in shape. Typical PML lesions are diffuse, located in the white matter mainly subcortical – involving U-fibers – with relative sparing of the periventricular white matter. Occasionally, extensions to gray matter have been
Conclusion
SWI and T2 GRE hypointensities in cortex and U-fibers adjacent to the white matter lesions seem highly prevalent in PML, irrespective of the delay between PML onset and the MRI and whatever the type of immunosuppression. QSM data suggest a paramagnetic effect. Other studies are mandatory to evaluate the incidence of these abnormalities in SWI and T2 GRE; they might be considered as new diagnostic tools in the context of PML, especially in the early stages of the disease.
Disclosure of interest
The authors declare that they have no competing interest.
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These authors contributed equally to this work.