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Incidence of progressive multifocal leukoencephalopathy in patients with rheumatoid arthritis: a national population-based study
  1. Elizabeth V Arkema1,
  2. Ronald F van Vollenhoven2,
  3. Johan Askling1,
  4. for the ARTIS Study Group
  1. 1Clinical Epidemiology Unit (T2), Department of Medicine,Karolinska Institutet, Stockholm, Sweden
  2. 2Unit for Clinical Therapy Research, Inflammatory Diseases (ClinTRID),Karolinska Institutet, Stockholm, Sweden
  1. Correspondence to Elizabeth V Arkema, Clinical Epidemiology Unit (T2), Department of Medicine, Karolinska Institutet, Stockholm SE-171 76, Sweden; earkema{at}


Background Cases of progressive multifocal leukoencephalopathy (PML), a rare but serious disease, have been reported in patients with rheumatoid arthritis (RA) in association with biological therapy, but little is known about the incidence of PML in patients with RA in the absence of treatment exposure.

Objective To estimate the incidence rate of PML in patients with RA compared with the general population, with and without exposure to biological agents.

Methods Patients with adult onset RA, exposure to biological agents and a diagnosis of PML from 1999 through 2009 were identified from national registries and linked using each Swedish resident's unique personal identification number. General population comparators matched on age, sex and county were also identified. Crude and age- and sex-standardised incidence rates (cases per 100 000 person-years) were calculated with 95% CI.

Results 66 278 patients with RA and 286 949 general population comparators were included in the study. The incidence rate of PML in the overall RA population was 1.0 (95% CI 0.3 to 2.5) compared with 0.3 (95% CI 0.1 to 0.6) in the general population. The difference in incidence rate was 0.7 (95% CI −0.3 to 17). Among all patients exposed to biological agents, only one patient was diagnosed with PML.

Conclusion Data from this national population-based cohort study suggest that patients with RA may have an increased rate of PML compared with the general population.

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  • The ARTIS Study Group E Baecklund, L Coster, C Forsblad-Elia, N Feltelius, P Geborek, L Jacobsson, L Klareskog, S Lindblad, S Rantapaa-Dahlqvist, T Saxne and R van Vollenhoven.

  • Funding Financial support for this study was obtained from the Swedish Research Council, the Swedish Cancer Society and from Stockholm County Council, from the Swedish Foundation for Strategic Research and from the Swedish COMBINE inflammation research consortium. The ARTIS register has agreements with Wyeth-Ayerst, Schering-Plough, Abbott Immunology, Roche, and Bristol Myer Squibb. The authors were in charge of and solely responsible for all data collection, analysis, interpretation and writing of the manuscript, without any constraints exerted from the agencies or companies that provided financial support for the study or for ARTIS. The South Swedish Anti-TNF Register has received funding from King Gustav V, Österlund and Kock Foundations, Reumatikerförbundet and from the Medical Faculty, Lund University. Financial support for the Early RA register was provided by the Swedish National Board of Health and Welfare.

  • Competing interests None.

  • Patient consent Not obtained.

  • Ethics approval Ethics approval was obtained from the Karolinska Institutet.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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