Objectives Mixed connective tissue disease (MCTD) is an immune-mediated, systemic disorder of unknown aetiology. As the epidemiology of the disease is largely unknown, the authors performed a nationwide cross-sectional retrospective study to assess the prevalence and incidence of MCTD in Norway.
Methods Every adult patient (≥18 years) with MCTD seen at one of the departments of rheumatology was reviewed for inclusion. Only patients who satisfied the following four criteria were included: clinical diagnosis of MCTD verified by a rheumatologist; positive serum anti-ribonucleoprotein antibody test; fulfilment of at least one of three of following criteria sets: the modified Sharp's criteria, the criteria of Alarcón-Segovia and Villareal and those of Kasukawa; and exclusion of other connective tissue diseases.
Results The four inclusion criteria were fulfilled by 147 adult Caucasian patients. The female to male ratio was 3.3 and the mean age at diagnosis of adult-onset MCTD was 37.9 years (95% CI 35.3 to 40.4 years). At the end of 2008, the point prevalence of living adult MCTD patients in Norway was 3.8 (95% CI 3.2 to 4.4) per 100 000 adults. The incidence of adult-onset MCTD in Norway during the period from 1996 to 2005 was 2.1 (95% CI 1.7 to 2.5) per million per year.
Conclusions MCTD has a female predominance and the incidence and prevalence of MCTD is low, and lower than reported figures for polymyositis, dermatomyositis, systemic sclerosis and systemic lupus erythematosus. The prevalence estimates were similar across the three criteria sets of MCTD.
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↵* The members of the PAHNORI Study Group are listed at the end of the paper.
Funding This study was supported by grants from the Norwegian Rheumatism Association and the Scandinavian Rheumatology Research Foundation.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the Regional Committee for Research Ethics in the Southern and Eastern Norway Regional Health Authority and the Norwegian Social Science Data Services.
Provenance and peer review Not commissioned; externally peer reviewed.
PAHNOR1 Study Group Åse Stavland Lexberg, Department of Rheumatology, Buskerud Hospital, Drammen, Norway; Kari Time, Haugesund Sanitetsforeningens Revmatismesykehus, Haugesund, Norway; Alvilde Sofie Strand Dhainaut, Department of Rheumatology, St Olavs Hospital, Trondheim University Hospital, Trondheim, Norway; Liv-Turid Bertelsen, Department of Rheumatology, Haukeland University Hospital, Bergen, Norway; Øyvind Palm, Lamya Samir Noori Garabet, Department of Rheumatology, Østfold Hospital, Moss, Norway; Karen Irgens, Department of Rheumatology, Ålesund Hospital, Ålesund, Norway; Andrea Becker-Merok, Department of Rheumatology, Institute of Clinical Medicine, University of Tromsø, Tromsø, Norway; Jan Leidulf Nordeide, Department of Rheumatology, Førde Central Hospital, Førde, Norway; Villy Johnsen, Department of Rheumatology, Sørlandet Hospital, Kristiansand, Norway; Sonja Pedersen, Department of Rheumatology, Nordland Hospital, Bodø, Norway; Anne Prøven, Department of Rheumatology, Martina Hansens Hospital, Baerum, Norway; Sven Gøran Sidenvall, Department of Rheumatology, Innlandet Hospital, Kongsvinger, Norway.