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Progressive multifocal leukoencephalopathy (PML) is a severe adverse event in patients with multiple sclerosis (MS) treated with natalizumab. Brain MRI can detect small PML lesions at an early disease stage.1 Therefore, MRI screening is recommended for patients at high risk of developing PML.2 Diagnosis of PML is confirmed by brain biopsy or detection of JC virus (JCV) DNA from cerebrospinal fluid (CSF).3 However, in spite of using ultrasensitive quantitative PCR (qPCR) protocols, patients with PML can be JCV DNA negative in CSF, hampering the diagnosis. Recently, we demonstrated that the detection of intrathecally produced anti-JCV IgG antibodies is highly specific for diagnosis of PML, making the so-called CSF JCV antibody index (AIJCV) a candidate tool for earlier diagnosing of PML in a proportion of natalizumab-associated PML patients.4
The aim of this study was to assess the value of the AIJCV in a case series of natalizumab-treated patients with MS undergoing enhanced MRI pharmacovigilance for PML.
Patients and methods
Natalizumab-treated MS patients screened for PML using MRI (T2, fluid attenuation inversion recovery (FLAIR), diffusion weighted imaging) at the VU University Medical Center Amsterdam, and referrals, were included in the study. Patients with MRI suspicion of PML and a serum/CSF pair for assessment of the AIJCV at time of first MRI suspicion of PML were eligible. JCV DNA by qPCR and the AIJCV in CSF were determined at the Institute of Virology, University of Düsseldorf, Germany, and methods and cut-points (1.5 for the AIJCV) were applied as recently described.4 The study was approved by the local institutional review board, and written informed consent was obtained from all participants.
Basic characteristics of the patients included are provided in the online supplementary table. Median age was 46 years, and five of eight patients (63%) were female. Six out of eight patients (75%) were judged asymptomatic by referring clinicians at time of first PML suspicion on MRI. All patients had been treated with natalizumab for >24 months, presented with MRI lesions suggestive of PML at time of first CSF analysis, and were JCV seropositive as assessed by Stratify-JCV®.5
CSF findings and resulting diagnostic certainty at time of PML suspicion
At time of PML suspicion on MRI, JCV DNA by qPCR was undetectable in four of the eight cases (50%, online supplementary table). Two patients (25%) had a positive AIJCV (>1.5) at time of first PML suspicion, of which case 3 was JCV qPCR positive and case 7 JCV qPCR negative. Applying published PML diagnostic criteria to these cases,3 only case 1 classified as ‘definite PML’ at time of MRI suspicion of PML (+clinical features, +MRI findings and +JCV DNA in CSF), whereas cases 2, 3 and 4 would be termed ‘probable PML’ (–clinical features, +MRI finding and +JCV DNA in CSF). The symptomatic case 6 (+clinical features, +MRI findings and –JCV DNA) would be judged ‘possible PML’, while cases 5, 7, and 8 with the mere MRI suspicion (–clinical features, +MRI findings and –JCV DNA in CSF) would be termed ‘not PML’.
Evidence of PML during follow-up in patients initially negative for JCV DNA in CSF
Of the four patients with a negative JCV PCR in CSF at the time of MRI suspicion of PML, two patients had additional CSF samples taken during follow-up. Case 5 displayed a positive JCV qPCR result in CSF during re-testing, thereby confirming the diagnosis of PML to ‘definite PML’. In case 6, a follow-up CSF sampling at months 2 and 3 remained negative for JCV DNA in CSF, but had a positive AIJCV at month 3. In case 7, despite the negative qPCR at time of PML suspicion on MRI, initial CSF sampling already displayed a positive AIJCV, supporting the diagnosis of PML. The cases of ‘possible PML’ (cases 6 and 8; reported as symptomatic at suspicion of PML, or during follow-up by the treating physician) or ‘not PML’ (case 7; reported asymptomatic also during follow-up) are considered having PML by the authors and treating physicians based on longitudinal MRI findings, as judged by an experienced neuroradiologistding and he thought (MPW). These patients were at high risk for PML development (ie, treatment duration >24 months and JCV seropositive), did not show MRI evidence of acute or new MS disease activity prior to PML diagnosis, and displayed a lesion evolution of the suspected PML lesion on follow-up scans highly suspicious of PML, including signs of PML immune reconstitution inflammatory syndrome (figure 1). Nonetheless, as first PML suspicion on MRI had occurred 4.5 months after natalizumab cessation in case 7 and no follow-up CSF was obtained, return of MS disease activity as differential diagnosis cannot be completely excluded in this case.
As per American Academy of Neurology diagnostic criteria, definite PML is a symptomatic disease confirmed by MRI and the detection of JCV DNA in CSF.3 This view is challenged by the application of MRI as a screening tool for early detection of PML. These patients can show localised disease on MRI (not multifocal as the acronym PML may imply), and a majority is asymptomatic. Furthermore, in our study half of the patients had negative JCV DNA findings in CSF at time of first MRI suspicion of PML. Importantly, if JCV DNA remains undetectable and brain biopsy is not performed, such cases classify as ‘possible’ or ‘not PML’, despite the strong MRI suspicion of PML. Consequently, these cases will not appear in PML statistics of confirmed cases, and consecutive management decisions (eg, plasma exchange in case of PML; continuation/switch of immune suppression in case of MS relapse) may be challenging. Our data suggests that detection of an intrathecal IgG antibody response towards JCV (positive AIJCV) may increase the sensitivity of CSF assessment for diagnosis of PML in patients with MRI suspicion of PML and during follow-up. Due to the limited size of this study, and the previous absence of a positive AIJCV in non-PML patients with MS during continued natalizumab therapy,4 we did not include a control group for this case series, and thus were unable to formally assess diagnostic specificity. However, this limitation refers to the CSF AIJCV and the JCV DNA detection from CSF by qPCR, making comprehensive studies in larger cohorts highly desirable to re-define the case definition of PML when MRI screening is used for early detection of PML.
The study was supported by a grant of the European Charcot Foundation, and the Hertie-Foundation to CW (P1150063). We are grateful to our collaborators: Bob W van Oosten and Chris H Polman (VU University Medical Center, Amsterdam, The Netherlands), Dorine A Siepman and Rogier Hintzen (Erasmus MC, University Medical Center Rotterdam, The Netherlands), Jop Mostert (Rijnstate Hospital, Department of Neurology, Arnhem, The Netherlands), Wibe Moll (Maasstad Hospital, Rotterdam, The Netherlands), Alex EL van Golde (ZGT Hospital, Almelo, The Netherlands), Stephan TFM Frequin (St Antonius Hospital, Nieuwegein, The Netherlands), Paul AD Bouma (Tergooi, Blaricum, Hilversum, The Netherlands), Bénédicte Quivron (CH Jolimont, La Louvière, Belgium), Jean Braeckeveldt (Epicura, Baudour, Belgium), Erik van Munster and Jeroen van Eijk (Department of Neurology, Jeroen Bosch Ziekenhuis, ‘s-Hertogenbosch, The Netherlands), Thea Heersema (Department of Neurology, University Medical Center Groningen, Groningen, The Netherlands), Jaap de Graaf (Isala Hospital, Zwolle, The Netherlands) and Raymond MM Hupperts (Zuyderland Medical Center, Sittard, The Netherlands).
Contributors Study concept and design: CW, OA and MPW. Acquisition and analysis of data: all. Drafting of manuscript: CW, MTW. Critical revision of the manuscript for important intellectual content: all.
Competing interests CW: consulting and/or research funding: Bayer, Biogen, Novartis, TEVA. HPH: received honoraria for consulting and speaking at symposia from Bayer, Biogen, Genzyme, Merck Serono, Novartis Pharma, Roche and Teva Sanofi-Aventis. JK: accepted speaker and consulting fees from Merck Serono, Biogen, TEVA, Genzyme, Roche and Novartis. OA: accepted speakers honoraria and research funding from Biogen. MPW: accepted speaker and consulting fees from Biogen, Novartis, Roche and Genzyme.
Patient consent All patients signed a written informed consent stating that data and imaging can be used for research and education, approved by the local institutional review board at VUmc.
Provenance and peer review Not commissioned; externally peer reviewed.
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