title: Inverse comorbidity in multiple sclerosis: Findings in a complete nationwide cohort.
abstract: BACKGROUND
  Inverse comorbidity is disease occurring at lower rates than expected among persons with a given index disease. The objective was to identify inverse comorbidity in MS.
  
  
  METHODS
  We performed a combined case-control and cohort study in a total nationwide cohort of cases with clinical onset of MS 1980-2005. We randomly matched each MS-case with five population controls. Comorbidity data were obtained from multiple, independent nationwide registries. Cases and controls were followed from January 1977 to the index date, and from the index date through December 2012. We controlled for false discovery rate and investigated each of eight pre-specified comorbidity categories: psychiatric, cerebrovascular, cardiovascular, lung, and autoimmune comorbidities, diabetes, cancer, and Parkinson's disease.
  
  
  RESULTS
  A total of 8947 MS-cases and 44,735 controls were eligible for inclusion. We found no inverse associations with MS before the index date. After the index date, we found a decreased occurrence of chronic lung disease (asthma and chronic obstructive pulmonary disease) (HR 0.80 (95% CI 0.75-0.86, p<0.00025)) and overall cancer (HR 0.88 (95% CI 0.81-0.95, p=0.0005)) among MS-cases.
  
  
  CONCLUSIONS
  This study showed a decreased risk of cancers and pulmonary diseases after onset of MS. Identification of inverse comorbidity and of its underlying mechanisms may provide important new entry points into the understanding of MS.
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark; The Danish Multiple Sclerosis Registry, Department of Neurology, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark. Electronic address: anja.thormann.01@regionh.dk.
authors.forename: Anja
authors.initials: A
authors.lastname: Thormann
authors.affiliation: The Danish Multiple Sclerosis Registry, Department of Neurology, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark; Department of Clinical Epidemiology, Clinical Institute, University of Aarhus, Olof Palmes Allé 43-45, DK-8200 Aarhus N, Denmark.
authors.forename: Nils
authors.initials: N
authors.lastname: Koch-Henriksen
authors.affiliation: The Danish National Institute of Public Health, University of Southern Denmark, Øster Farimagsgade 5A, DK-1353 Copenhagen K, Denmark.
authors.forename: Bjarne
authors.initials: B
authors.lastname: Laursen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Per Soelberg
authors.initials: PS
authors.lastname: Sørensen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark; The Danish Multiple Sclerosis Registry, Department of Neurology, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Melinda
authors.initials: M
authors.lastname: Magyari
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D015897:Comorbidity; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications / Q000453:epidemiology*; D016016:Proportional Hazards Models; D012042:Registries; D055815:Young Adult
keywords: Comorbidity; Diametrical diseases; Epidemiology; Inverse comorbidity; Multiple sclerosis