Background/Purpose: The prevalence of psoriatic arthritis (PsA) varies substantially world-wideand is highest among Caucasians of European descent. Studies from India suggest that patients with PsA have a milder disease. Comparing disease phenotype across ethnicities can provide insight into mechanisms underlying disease severity. We aimed to determine whether demographic and disease characteristics differed in PsA patients of South Asian ethnicity compared to those of European ethnicity Methods: The study was conducted at a PsA clinic in a North American city with a diverse ethnic composition. Patients are assessed every 6-12 months according to a standard protocol. Prospectively collected data were retrieved from the clinic database. The distribution of ethnicities within the cohort was determined. The demographic and disease characteristics of those with South Asian ethnicity were compared to those of European ethnicity using chi-squared tests and unpaired t-test. Subsequently, each patient of South Asian ethnicity was matched by gender, age, duration of PsA and year of entry to clinic, to 3 patients of European ethnicity and the disease characteristics compared using McNemar and paired t-tests.

Results: The distribution of the 1184 patients in the cohort were as follows: European 1037 (88%), South Asian 59 (5%), Chinese 26 (2.2%), Black 12 (1%), Filipino 12 (1%), Hispanic 7 (0.6%), South-east Asian 4 (0.3%) , Korean 2 (0.2%), Aboriginal 1 (0.1%) and other/mixed 24 (2%). Overall patients of South Asian descent had shorter duration of psoriasis, lower family history of psoriasis, lower family history of PsA, lower prevalence of obesity, lower exposure to biologic agents and NSAIDs as well as lower prevalence of nail psoriasis and severe radiographic damage (defined as grade 4 damage according to the Steinbrocker method) compared to patients of European descent. The summary of results of the matched analysis comparing patients of South Asian descent to those of European descent is presented in Table 1. Patients of South Asian descent had lower tender joint counts, less number of joints with severe damage, lower frequency of treatment with biologics, lower frequency of HLA*B27 and  worse SF-36 MCS scores, compared to matched patients of European descent. Although they had lower prevalence of obesity, the prevalence of diabetes and hyperlipidemia was higher.

Conclusion: Although PsA patients of South Asian descent report higher HAQ scores, and have more tender joints,  radiographic joint damage appears to be less severe and they are less likely to be treated with biologic agents than patients of European descent. Although less likely to be obese, they have higher prevalence of diabetes and hyperlipidemia. Ethnic differences in disease manifestations may have an impact on long-term outcomes of patients with PsA.

Table 1. Summary of the results of the matched-pair analyses between subjects of South Asian ethnicity and those of European ethnicity