Epidemiology of psoriasis and palmoplantar pustulosis: a nationwide study using the Japanese national claims database.
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.


SETTINGS
Patients with a psoriasis or PPP diagnosis code between April 2010 and March 2011 were identified using a Japanese national database.


PARTICIPANTS
565 903 patients with psoriasis or PPP were identified. No patient was excluded.


PRIMARY AND SECONDARY OUTCOME MEASURES
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.
['Kubota|Kiyoshi|K|', 'Kamijima|Yukari|Y|', 'Sato|Tsugumichi|T|', 'Ooba|Nobuhiro|N|', 'Koide|Daisuke|D|', 'Iizuka|Hajime|H|', 'Nakagawa|Hidemi|H|']
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 D008297:Male D008875:Middle Aged D015995:Prevalence D011565:Psoriasis D055815:Young Adult
palmoplantar pustulosis database Japan