Influence of age of onset of psoriasis on prevalence and clinical characteristics of psoriatic arthritis (according to the registry of patients with psoriasis)

Сlinical, immunological and genetic differences between patients with early and late onset psoriasis are reported. Comparative studies of clinical characteristics of psoriatic arthritis according to age of psoriasis onset (skin manifestation) are lacking. Aim – to compare the prevalence and clinical characteristics of psoriatic arthritis depending on age of psoriasis onset (skin manifestation) in patients included to the psoriasis patient registry of Russian Society of Dermatovenereologists and Cosmetologists. Materials and methods . Prevalence of psoriatic arthritis in 3,227 patients with psoriasis aged 18 years and older was calculated. Comparison of the clinical characteristics of psoriatic arthritis according to the age of onset of psoriasis was performed on 916 patients with psoriasis and psoriatic arthritis. The U-test was used to compare quantitative variables. To identify the association between qualitative variables, the χ2 test was used; odds ratio and 95% confidence interval were calculated, unadjusted and adjusted for other independent variables. Results . In the majority of patients (73%), psoriasis manifested before the age of 40. Psoriatic arthritis at the time of inclusion to the registry was diagnosed in 31.7% of patients with early onset psoriasis and in 19.5% of patients with late onset psoriasis (p=0.0005). The odds of having psoriatic arthritis were almost two times lower in patients with late onset psoriasis (p=0.0005). When adjusted for sex and age, the odds of having psoriatic arthritis among patients with late onset psoriasis became 4 times lower than in patients with early onset psoriasis (p=0.0005). However, when adjusted for sex and duration of psoriasis, the odds ratio lost its statistical significance. The axial involvement (32.1% vs 20.5%; p=0.003) and the involvement of foot joints (59.7% vs 51.5%; p=0.048) was more likely in patients with early onset psoriasis. The odds ratio for axial involvement was still statistically significant when adjusted for other independent variables. Conclusions . Age of onset of psoriasis before 40 years of age is associated with more frequent axial involvement in psoriatic arthritis.