Body Surface Area Affected by Psoriasis and the Risk for Psoriatic Arthritis

A Prospective Population-Based Cohort Study

Alexis Ogdie; Daniel B. Shin; Thorvardur Jon Love; Joel M. Gelfand


Rheumatology. 2022;61(5):1877-1884. 

In This Article

Abstract and Introduction


Objective: Increasing psoriasis severity has been associated with comorbidities including cardiovascular disease. The objective of this study was to examine the association of psoriasis severity with the development of PsA.

Methods: A prospective population-based cohort study was performed within The Health Improvement Network, a UK medical record database. Patients aged 25–60 years with a code for psoriasis were randomly selected between 2008 and 2011. Questionnaires were sent to their general practitioners to confirm the diagnosis of psoriasis and provide the patient's approximate body surface area (BSA). Incidence of PsA was calculated by BSA, and Cox proportional hazard ratios were used to examine the risk of developing PsA by BSA category after adjusting for other covariates.

Results: Among 10 474 questionnaires sent, 9987 (95%) were returned, 9069 (91%) had confirmed psoriasis, and BSA was provided for 8881 patients: 52% had mild psoriasis, 36% moderate psoriasis and 12% severe psoriasis. The mean age was 46, and 49% were female. Mean follow-up time was 4.2 years (S.D. 2.1); the incidence of PsA was 5.4 cases per 1000 person-years. After adjusting for age and sex, BSA >10% [hazard ratio (HR) 2.01, 95% CI: 1.29, 3.13], BSA 3–10% (HR 1.44, 95% CI: 1.02, 2.03), obesity (HR 1.64, 95% CI: 1.19, 2.26) and depression (HR 1.68, 95% CI: 1.21, 2.33) were associated with incident PsA.

Conclusions: In this large prospective cohort study, BSA assessed by general practitioners was a strong predictor of developing PsA, and obesity and depression were additive risk factors.


Psoriasis is a common inflammatory skin condition associated with systemic inflammation that affects up to 2% of adults in North America and Europe.[1] As the total amount of psoriasis increases, as measured by body surface area (BSA), the risk for other chronic diseases such as coronary artery disease[2,3] and diabetes, as well as the risk for mortality, also increases.[4,5] Thus, measuring psoriasis severity in clinical practice can help risk-stratify patients who may be at increased risk for cardiometabolic disease. However, PsA is among the most common and impactful concomitant conditions in patients with psoriasis, affecting 10–30% of patients.[6,7] PsA is a chronic inflammatory arthritis that can cause significant disability. The early identification of PsA is important to improving long-term outcomes, including decreased radiographic damage and improved response to therapy.[8,9] However, early identification remains an important challenge.[10] Compared with other rheumatic diseases, PsA has a substantial advantage: most patients with PsA first developed psoriasis.[6] If general practitioners (GPs) could risk-stratify patients with psoriasis and integrate that knowledge into the assessment of joint complaints in this patient population, they may decrease the prolonged time to diagnosis in PsA.[11–13]

As with cardiometabolic disease, psoriasis severity has been identified as a potential risk factor for PsA. Only two cohort studies have addressed whether psoriasis severity increases the risk for PsA: one retrospective cohort study used number of sites of psoriasis as a measure of severity, and the other studied a dermatology patient population and used the Psoriasis Area and Severity Index (PASI), a measure that is too complex to implement into primary care clinical practice.[14,15] No prospective population-based cohort studies have fully addressed the risk for PsA by psoriasis severity as measured by BSA.[6]

Beyond psoriasis severity, one of the consistently identified risk factors for PsA is obesity.[16–19] Metabolic conditions, including hyperlipidaemia, have also been associated with the development of PsA.[20] Obesity and metabolic conditions are known to be associated with more severe psoriasis and thus may be potential confounders in the relationship between psoriasis severity and PsA.[21] It remains unclear whether obesity and psoriasis severity are independent risk factors for PsA that each contribute to risk. The objective of this paper is to examine the association of BSA (an objective measure of psoriasis severity), obesity and other potential risk factors with the development of PsA in a prospective cohort of patients with psoriasis.