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Low signal intensity in U-fiber identified by susceptibility-weighted imaging in two cases of progressive multifocal leukoencephalopathy

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Highlights

  • This report describes two PML cases showing characteristic findings on SWI.

  • This is the first report of a new finding of SWI in PML.

  • SWI showed low signal intensities in U-fibers, progressing with disease progression.

  • This finding may be useful for the diagnosis of PML.

Abstract

Magnetic resonance imaging (MRI) is a useful tool for diagnosing and monitoring progressive multifocal leukoencephalopathy (PML). Although characteristic MRI findings of PML are well known, we noted a potential new finding for this disease on susceptibility-weighted imaging (SWI). Two patients with PML were studied and followed using MRI. SWI revealed low signal intensities in U-fibers adjacent to the white matter lesions of PML. These findings progressed along with the disease progression. The cause underlying these findings remains unclear. This new finding suggests that SWI is useful for the diagnosis of PML. It can provide a helpful clue in a clinical setting.

Introduction

Progressive multifocal leukoencephalopathy (PML), a progressive demyelinating disease of the brain caused by oligodendrocyte, astrocyte, and neuron damage resulting from reactivation of JC virus (JCV) [1], was once regarded as a fatal disease characterized by progressive neurological deficits, leading to death within 2.5–4 months of diagnosis in the absence of treatment [2]. Recently however, reports have described that in certain clinical conditions such as natalizumab therapy in multiple sclerosis patients, an early PML diagnosis, preferably in a presymptomatic/asymptomatic stage, but even in a symptomatic stage, is associated with a favorable prognosis [3], [4]. The diagnosis of PML is based on clinical information and detection of JCV in cerebrospinal fluid (CSF) or brain tissue, but a combination of specific findings from magnetic resonance imaging (MRI) enables us to suspect PML, including multifocal white matter lesions involving U-fibers, faint or absent peripheral enhancement of lesions, minimal or no mass effect, and hyperintensity on the periphery of lesions on diffusion-weighted imaging (DWI) [5], [6]. Regarding the diagnosis of PML, the official American Academy of Neurology (AAN) criteria on PML diagnosis were proposed recently based on a combination of data related to clinical features, imaging findings, and CSF polymerase chain reaction (PCR) JCV [7]. For PML diagnosis, MRI is therefore regarded as an important tool. To date, no report has described specific findings for PML obtained using susceptibility-weighted imaging (SWI). This report is the first of a potential new finding by SWI in two patients with PML.

Section snippets

Case 1

A 56-year-old man treated for repeated erysipelas and otitis externa was hospitalized with left paresis. Neurological examination showed left unilateral spatial neglect. Initial brain MRI revealed a hyperintense lesion on DWI in the subcortical lesion of the right occipital lobe. The initial diagnosis was acute brain infarction. He was treated with aspirin and edaravone for 2 weeks. He subsequently experienced repeated infection, such as that of Pneumocystis carinii pneumonia. The left paresis

MRI findings in the two PML cases

These two patients with PML underwent serial MR examinations with 3.0-T MRI (Achieva; Philips Health Care, Best, The Netherlands), including T1-weighted imaging, T2-weighted imaging, 3D FLAIR, DWI, and SWI. MRI sequences other than SWI showed typical findings for PML, such as hypointense lesions on T1-weighted imaging, hyperintense lesions on T2-weighted imaging and 3D FLAIR in subcortical white matter, and peripheral hyperintensity on DWI (Fig. 1, Fig. 2, Fig. 3). Neither a mass effect nor

Discussion

Brain MRI has been regarded as an important tool for PML diagnosis and monitoring [5], [6], [8]. Several MRI findings suggesting PML have been reported, including an asymmetrical lesion located predominantly in the subcortical white matter involving U-fibers, faint or absent peripheral enhancement, minimal or no mass effect considering lesion size, and hyperintensity on DWI at the edge of lesions correlated with active infection [5], [6]. Nevertheless, no report in the English-language

Conflict of interest

No author declares a potential conflict of interest.

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    A typical active PML lesion shows a central core with a low signal on DWI, high signal on apparent diffusion coefficient (ADC) map and high signal on DWI consistent with restricted diffusion on the periphery [8]. SWI low signal intensities in U-fibers adjacent to the white matter lesions of PML had been recently described in two patients with PML [5]. Our study suggests a high prevalence of SWI low signal intensities in U-fibers and/or in the cortex adjacent to the white matter lesions of PML, independently of the nature of the immunosuppression: indeed all of our four patients had cortical and/or subcortical abnormalities on SWI.

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