title: A nationwide study of the epidemiology of relapsing polychondritis.
abstract: OBJECTIVE
  Relapsing polychondritis (RP) is a rare autoimmune inflammatory disease that attacks mainly cartilaginous structures or causes serious damage in proteoglycan-rich structures (the eyes, heart, blood vessels, inner ear). This study shows results regarding the epidemiology, progression, and associations of this highly variable disease by collecting all cases from a 124-million-person-year Central European nationwide cohort.
  
  
  METHODS
  We used the Hungarian Health Care Database to identify all persons with possible RP infection. We followed patients who had International Classification of Diseases 10th edition code M94.1 at least once in their inpatient or outpatient records between January 1, 2002 and December 31, 2013 in Hungary. We classified these patients into disease severity groups by their drug consumption patterns between January 1, 2010 and December 31, 2013. We analyzed the regional distribution of RP incidences as well. Overall maps of comorbidity are presented with network layouts.
  
  
  RESULTS
  We identified 256 patients with RP among cumulatively 11.5 million registered inhabitants. We classified these patients into four severity classes as "extremely mild" (n=144), "mild" (n=22), "moderate" (n=41), and "severe" (n=4). Two additional groups were defined for patients without available drug data as "suspected only" (n=23) and "confirmed but unknown treatment" (n=22). The age and sex distributions of patients were similar to worldwide statistics. Indeed, the overall survival was good (95% confidence interval for 5 years was 83.6%-92.9% and for 10 years was 75.0%-88.3% which corresponds to the overall survival of the general population in Hungary), and the associations with other autoimmune disorders were high (56%) in Hungary. Almost any disease can occur with RP; however, the symptoms of chromosomal abnormalities are only incidental. Spondylosis can be a sign of the activation of RP, while Sjögren syndrome is the most frequent autoimmune association. Regional distribution of incidences suggests arsenic drinking water and sunlight exposure as possible triggering factors.
  
  
  CONCLUSIONS
  The good survival rate of RP in Hungary is probably associated with the early diagnosis of the disease.
authors.affiliation: 3rd Department of Internal Medicine, Semmelweis University.
authors.forename: Anna
authors.initials: A
authors.lastname: Horváth
authors.affiliation: Regional Science Center, Faculty of Science, Eötvös Loránd University.
authors.forename: Nóra
authors.initials: N
authors.lastname: Páll
authors.affiliation: 3rd Department of Internal Medicine, Semmelweis University.
authors.forename: Katalin
authors.initials: K
authors.lastname: Molnár
authors.affiliation: National Healthcare Service Center.
authors.forename: Tamás
authors.initials: T
authors.lastname: Kováts
authors.affiliation: National Healthcare Service Center.
authors.forename: György
authors.initials: G
authors.lastname: Surján
authors.affiliation: MTA-ELTE Statistical and Biological Physics Research Group; Department of Biological Physics, Eötvös Loránd University Budapest, Hungary.
authors.forename: Tamás
authors.initials: T
authors.lastname: Vicsek
authors.affiliation: Regional Science Center, Faculty of Science, Eötvös Loránd University; MTA-ELTE Statistical and Biological Physics Research Group.
authors.forename: Péter
authors.initials: P
authors.lastname: Pollner
keywords: autoimmune comorbidity; cohort of Hungary; environmental factors; incidence rate; network representation; severity prevalence