title: Identification of subtypes of refractory asthma in Korean patients by cluster analysis.
abstract: BACKGROUND
  Refractory asthma, a subtype of asthma with uncontrolled symptoms despite antiasthma medications, is a heterogeneous syndrome with variable clinical features, presumably different etiologies, and pathophysiological mechanisms. The heterogeneity of refractory asthma, however, is poorly understood. We aimed to characterize refractory asthma and to improve our understanding of the heterogeneity of refractory asthma patients.
  
  
  METHODS
  We identified refractory asthma patients (n = 96) as defined by the American Thoracic Society's criteria from a cohort of Korean asthma patients (n = 2,187). Then, cluster analysis was conducted to classify subtypes of refractory asthma.
  
  
  RESULTS
  Among the study group, 4.4 % (n = 96) of all asthma patients had refractory asthma. Cluster analysis identified four distinct groups of refractory asthma. Age at onset was younger in clusters 1 and 2 than in clusters 3 and 4. Patients in cluster 1 had the most well-preserved pulmonary function; patients in cluster 2 had a female predominance and the most severe airway obstruction; patients in cluster 3 were mostly female and had the most enhanced bronchial hyperresponsiveness; and patients in cluster 4 were most male and tended to be cigarette smokers.
  
  
  CONCLUSIONS
  The current results suggest that refractory asthma is a heterogeneous syndrome and could be classified into four subtypes. Underlying pathogenesis and therapeutic approaches may differ for the different subtypes and further research is needed.
authors.affiliation: Division of Allergy and Respiratory Medicine, Genome Research Center for Allergy and Respiratory Diseases, Soonchunhyang University Bucheon Hospital, Gyeonggi-do, 420-767, Republic of Korea.
authors.forename: An Soo
authors.initials: AS
authors.lastname: Jang
authors.forename: Hyouk-Soo
authors.initials: HS
authors.lastname: Kwon
authors.forename: You Sook
authors.initials: YS
authors.lastname: Cho
authors.forename: Yun Jeong
authors.initials: YJ
authors.lastname: Bae
authors.forename: Tae Bum
authors.initials: TB
authors.lastname: Kim
authors.forename: Jong Sook
authors.initials: JS
authors.lastname: Park
authors.forename: Sung Woo
authors.initials: SW
authors.lastname: Park
authors.forename: Soo-Taek
authors.initials: ST
authors.lastname: Uh
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Choi
authors.forename: Yong-Hoon
authors.initials: YH
authors.lastname: Kim
authors.forename: Hyeon-Kyu
authors.initials: HK
authors.lastname: Hwang
authors.forename: Hee-Bom
authors.initials: HB
authors.lastname: Moon
authors.forename: Choon Sik
authors.initials: CS
authors.lastname: Park
mesh_terms: D000328:Adult; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use*; D001249:Asthma / Q000145:classification* / Q000188:drug therapy* / Q000453:epidemiology; D016000:Cluster Analysis; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010361:Patients / Q000145:classification; D056910:Republic of Korea / Q000453:epidemiology; D017211:Treatment Failure
chemical_list: D018927:Anti-Asthmatic Agents