title: Classification and implementation of asthma phenotypes in elderly patients.
abstract: BACKGROUND
  No attempt has yet been made to classify asthma phenotypes in the elderly population. It is essential to clearly identify clinical phenotypes to achieve optimal treatment of elderly patients with asthma.
  
  
  OBJECTIVE
  To classify elderly patients with asthma by cluster analysis and developed a way to use the resulting cluster in practice.
  
  
  METHODS
  We applied k-means cluster to 872 elderly patients with asthma (aged ≥ 65 years) in a prospective, observational, and multicentered cohort. Acute asthma exacerbation data collected during the prospective follow-up of 2 years was used to evaluate clinical trajectories of these clusters. Subsequently, a decision-tree algorithm was developed to facilitate implementation of these classifications.
  
  
  RESULTS
  Four clusters of elderly patients with asthma were identified: (1) long symptom duration and marked airway obstruction, (2) female dominance and normal lung function, (3) smoking male dominance and reduced lung function, and (4) high body mass index and borderline lung function. Cluster grouping was strongly predictive of time to first acute asthma exacerbation (log-rank P = .01). The developed decision-tree algorithm included 2 variables (percentage of predicted forced expiratory volume in 1 second and smoking pack-years), and its efficiency in proper classification was confirmed in the secondary cohort of elderly patients with asthma.
  
  
  CONCLUSIONS
  We defined 4 elderly asthma phenotypic clusters with distinct probabilities of future acute exacerbation of asthma. Our simplified decision-tree algorithm can be easily administered in practice to better understand elderly asthma and to identify an exacerbation-prone subgroup of elderly patients with asthma.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea; Institute of Allergy and Clinical Immunology, Seoul National University Medical Research Center, Seoul, Korea.
authors.forename: Heung-Woo
authors.initials: HW
authors.lastname: Park
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea; Institute of Allergy and Clinical Immunology, Seoul National University Medical Research Center, Seoul, Korea.
authors.forename: Woo-Jung
authors.initials: WJ
authors.lastname: Song
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Bundang, Korea.
authors.forename: Sae-Hoon
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Pusan National University School of Medicine, Pusan, Korea.
authors.forename: Hye-Kyung
authors.initials: HK
authors.lastname: Park
authors.affiliation: Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Sang-Heon
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Chosun University Medical School, Gwangju, Korea.
authors.forename: Yong Eun
authors.initials: YE
authors.lastname: Kwon
authors.affiliation: Department of Allergy and Clinical Immunology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Hyouk-Soo
authors.initials: HS
authors.lastname: Kwon
authors.affiliation: Department of Allergy and Clinical Immunology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Tae-Bum
authors.initials: TB
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Bundang, Korea.
authors.forename: Yoon-Seok
authors.initials: YS
authors.lastname: Chang
authors.affiliation: Department of Allergy and Clinical Immunology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: You-Sook
authors.initials: YS
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Byung-Jae
authors.initials: BJ
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Dankook University College of Medicine, Cheonan, Korea.
authors.forename: Young-Koo
authors.initials: YK
authors.lastname: Jee
authors.affiliation: Department of Internal Medicine, Soonchunhyang University School of Medicine, Bucheon, Korea.
authors.forename: An-Soo
authors.initials: AS
authors.lastname: Jang
authors.affiliation: Department of Allergy and Clinical Immunology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Dong-Ho
authors.initials: DH
authors.lastname: Nahm
authors.affiliation: Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Jung-Won
authors.initials: JW
authors.lastname: Park
authors.affiliation: Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Ho Joo
authors.initials: HJ
authors.lastname: Yoon
authors.affiliation: Department of Internal Medicine, Ewha Womans University College of Medicine, Seoul, Korea.
authors.forename: Young-Joo
authors.initials: YJ
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Chung-Ang University College of Medicine, Seoul, Korea.
authors.forename: Byoung Whui
authors.initials: BW
authors.lastname: Choi
authors.affiliation: Department of Allergy and Clinical Immunology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Hee-Bom
authors.initials: HB
authors.lastname: Moon
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea; Institute of Allergy and Clinical Immunology, Seoul National University Medical Research Center, Seoul, Korea. Electronic address: shcho@snu.ac.kr.
authors.forename: Sang-Heon
authors.initials: SH
authors.lastname: Cho
mesh_terms: D000368:Aged; D000402:Airway Obstruction / Q000145:classification / Q000453:epidemiology*; D000465:Algorithms; D001249:Asthma / Q000145:classification / Q000453:epidemiology*; D016000:Cluster Analysis; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007723:Korea; D008297:Male; D010641:Phenotype; D011379:Prognosis; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking