Background/Purpose:

Psoriatic Arthritis (PsA) is a heterogeneous disease with widely varying clinical features and outcomes. Phenotypic heterogeneity may reflect genetic heterogeneity. We aimed to investigate whether the interval between the onset of psoriasis and PsA could be used to define more homogeneous subsets of PsA.

Methods:

Data on the age at onset of psoriasis and PsA, clinical and radiographic features at baseline as well as HLA B*27 and C*06 status was obtained from a large well-phenotyped PsA cohort. Patients were divided into 4 quartiles based on the time interval between the onset of psoriasis and the onset of PsA. The distribution of the above HLA alleles between the 4 quartiles was investigated. Subsequently, the patients were divided into 2 groups by combing the first two and the last two quartiles. Differences between the clinical and radiographic features at baseline (t-tests, chi-squared test, logistic regression) between the two groups were then investigated. 

Results:

1202 patients [56.7% males, mean (s.d.) age at first visit 47.4 (13.3) years, duration of psoriasis 18.2 (13.3) years, duration of PsA  10.1 (9.0) years] were distributed into the following 4 quartiles based on the time interval between onset of psoriasis and PsA- quartile 1: <0 years (n=318 patients, 26.5%), quartile 2: 0-5 years (n=291 patients, 24.2%), quartile 3: 5-13 years (n=262 patients, 21.8%) and quartile 4: >=13 years (n=331 patients, 27.5%). The distribution of HLA C*06 by quartile was 15.5%, 23.0%, 29.7% and 36.3% (trend test p-value <0.0001), while that of HLA B*27 was 21.2%, 18.1%, 15.6%, and 13.1% (trend test p-value =0.01), respectively.

At baseline, compared to group 1 (quartile 3 and 4), group 0 (quartile 1 and 2) had a significantly higher proportion of males, older age at onset of psoriasis but lower age at onset of PsA, lower PASI scores, higher prevalence of dactylitis, radiographic joint damage and patients treated with NSAIDs. There was no significant difference in the tender and swollen joint counts, ESR and the proportion of patients treated with DMARDs and biologics (Table 1). Since the proportion of patients positive for HLA B*27 and C*06 were different between the two groups, we examined whether the differences remained after adjusting for HLA status. After adjusting for HLA B*27 positivity there were no significant differences in the proportion of males, age at onset of PsA, and PASI score. When adjusting for HLA C*06 there was no difference in the proportion of males. When adjusting for HLA B*27 and C*06 differences between the two groups in age at onset of psoriasis, age at onset of PsA, PASI score, dactylitis and radiographic damage remained significant (p<0.05).

Conclusion:

There are differences in the clinical phenotype of PsA when taking the interval between the onset of psoriasis and PsA into account. These differences are not fully explained by the differences in the HLA -B*27 and –C*06 status between the two groups.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/time-interval-between-the-onset-of-psoriasis-and-the-onset-of-psoriatic-arthritis-may-define-disease-subsets/