title: Epidemiology of psoriasis and palmoplantar pustulosis: a nationwide study using the Japanese national claims database.
abstract: OBJECTIVE
  The primary objective was to estimate the national prevalence of psoriasis and palmoplantar pustulosis (PPP) in Japan. Secondary objectives were to determine (1) whether psoriasis and PPP disease activity varies by season, and (2) whether disease severity is associated with concurrent diabetes mellitus, hyperlipidaemia and hypertension.
  
  
  METHODS
  Patients with a psoriasis or PPP diagnosis code between April 2010 and March 2011 were identified using a Japanese national database.
  
  
  METHODS
  565 903 patients with psoriasis or PPP were identified. No patient was excluded.
  
  
  METHODS
  National prevalence was calculated using census data. We estimated the difference in the proportion of patients who used healthcare services, as a proxy for disease activity, between the hot and cold seasons and the difference in the standardised prevalence of comorbidities between severe and mild disease. The measures were estimated separately for the two broad disease categories of psoriasis and PPP but not in all patients as planned because the two disease categories had major differences.
  
  
  RESULTS
  The national prevalence of psoriasis and PPP was 0.34% (95% CI 0.34% to 0.34%) and 0.12% (0.12% to 0.12%), respectively. The difference in the proportion of patients who used healthcare services in the hot compared to the cold season was -0.3% (-0.5% to -0.1%) for psoriasis and 10.0% (9.8% to 10.3%) for PPP. The difference in the standardised prevalence between severe and mild psoriasis was 3.1% (2.7% to 3.4%), 3.2% (2.8% to 3.6%) and 5.1% (4.7% to 5.6%) for concurrent diabetes mellitus, hyperlipidaemia and hypertension, respectively. No significant difference in the prevalence of comorbidity was observed for PPP.
  
  
  CONCLUSIONS
  The national prevalence, seasonal variation in disease activity and prevalence of comorbidities in Japanese patients with psoriasis and PPP estimated in this descriptive study may be used as basic information for future studies.
authors.affiliation: Department of Pharmacoepidemiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan NPO Drug Safety Research Unit Japan, Tokyo, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kubota
authors.affiliation: Department of Pharmacoepidemiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan NPO Drug Safety Research Unit Japan, Tokyo, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Kamijima
authors.affiliation: Department of Pharmacoepidemiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan Faculty of Pharmaceutical Sciences, Tokyo University of Science, Chiba, Japan.
authors.forename: Tsugumichi
authors.initials: T
authors.lastname: Sato
authors.affiliation: Department of Pharmacoepidemiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan Department of Clinical Pharmacy, Nihon University School of Pharmacy, Chiba, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Ooba
authors.affiliation: Department of Clinical Epidemiology and Systems, Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Koide
authors.affiliation: Department of Dermatology, Asahikawa Medical University, Hokkaido, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Iizuka
authors.affiliation: Department of Dermatology, Jikei University, School of Medicine, Tokyo, Japan.
authors.forename: Hidemi
authors.initials: H
authors.lastname: Nakagawa
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007344:Insurance Claim Reporting; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011565:Psoriasis / Q000453:epidemiology*; D055815:Young Adult
keywords: Japan; database; palmoplantar pustulosis