Myasthenia gravis epidemiology in a national cohort; combining multiple disease registries

Authors

  • J. B. Andersen,

    Corresponding author
    1. Department of Clinical Medicine, University of Bergen, Bergen, Norway
    • J. B. Andersen, Department of Clinical Medicine, Section for Neurology, University of Bergen, P.O. Box 7804, N-5020 Bergen, Norway

      Tel.: +47 55975092

      Fax: +47 55972761

      e-mail: Jintana.Andersen@k1.uib.no

      A. T. Heldal, Department of Neurology, Haukeland University Hospital, N-5021 Bergen, Norway

      Tel.: +47 55975077

      Fax: +47 55975165

      e-mail: anne.taraldsen.heldal@helse-bergen.no

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  • A. T. Heldal,

    Corresponding author
    1. Department of Clinical Medicine, University of Bergen, Bergen, Norway
    • J. B. Andersen, Department of Clinical Medicine, Section for Neurology, University of Bergen, P.O. Box 7804, N-5020 Bergen, Norway

      Tel.: +47 55975092

      Fax: +47 55972761

      e-mail: Jintana.Andersen@k1.uib.no

      A. T. Heldal, Department of Neurology, Haukeland University Hospital, N-5021 Bergen, Norway

      Tel.: +47 55975077

      Fax: +47 55975165

      e-mail: anne.taraldsen.heldal@helse-bergen.no

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  • A. Engeland,

    1. Division for Epidemiology, Department of Pharmacoepidemiology, Norwegian Institute of Public Health, Bergen, Norway
    2. Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway
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  • N. E. Gilhus

    1. Department of Clinical Medicine, University of Bergen, Bergen, Norway
    2. Department of Neurology, Haukeland University Hospital, Bergen, Norway
    Search for more papers by this author

Abstract

Objectives

There is a wide variation in reported prevalence and incidence of myasthenia gravis (MG). In this study, we aimed to evaluate the validity of two nationwide databases by comparing prevalence and incidence rates reported from three recent studies using the two databases as case-finding method.

Materials and methods

Two different Norwegian nationwide databases were used: the acetylcholine receptor antibody database (reference cohort) and the Norwegian Prescription Database (NorPD) (study cohort). Presence of acetylcholine receptor antibodies (AChR) is specific for MG. Up to 85% of MG patients are AChR antibody-positive. All samples from the whole country were tested at one laboratory. NorPD contains patient information on all prescriptions of pyridostigmine.

Results

Prevalence was 131 per million in the study cohort and 145 per million estimated from the reference cohort (Jan 1, 2008). No significant difference in prevalence between the study cohort and the reference cohort was found (SIR 1.1, 95% CI 1.0–1.2). The annual incidence rate was 16.0 per million in the study cohort and 8.8 per million estimated from the reference cohort, twofold more new MG patients were found in the study cohort compared to estimated figures from the reference cohort (SIR 1.8; 1.4–2.3).

Conclusions

This study confirms an optimal and unbiased case finding in both databases. Our calculated prevalence and incidence rates are in line with previous population-based studies. There was good agreement in prevalence reported from the two databases. The discrepancy in incidence is expected to diminish as years of study are increasing in NorPD.

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