Psoriatic arthritis affects 20-30% of patients with psoriasis. Few epidemiological data are available in France about its prevalence and its association with skin lesions and comorbidities.To assess the epidemiological aspects and the risk factors for psoriatic arthritis in children and adults in France.Two cross-sectional studies were conducted in France in children (χ-Psocar, 23 pediatric dermatology centers belonging to the SFDP, 1 year) and adults (Resopsocar, 29 dermatology centers belonging to GEM RESOPSO, 4 months) to study the link between psoriasis and cardiovascular and metabolic comorbidities.Three hundred and thirteen children (males: 47.6%; mean age: 9.4 yrs) and 1,954 adults (males: 56.0%; mean age: 48.5 yrs) with psoriasis were included, with 4.2% of the children and 21.0% of the adults presenting psoriatic arthritis. Prevalence increased with age: 2.2% of children, 14.2% of adolescents, and over 20% after 40 years. It decreased after the age of 70 years (19.4%). Regardless of age, arthritis was not associated with gender. In the children's group, rheumatism was associated with nail involvement (P=0.04) and disease severity (P=0.0004). Adult rheumatism was associated with generalized plaque psoriasis (P=0.002), disease severity (P0.0001), and obesity (P0.0001). Localized plaque psoriasis was less often associated with arthritis (P0.05).These two cross-sectional studies conducted in 2267 patients in France yielded information on the prevalence of joint involvement from infants to elderly subjects. It is the first study conducted in a single population to provide data for the whole population. Prevalence gradually increases with age, without gender difference, before decreasing in old age. We confirm the association of nail involvement in the first years of life, and of obesity in adults.
