Psoriatic Arthritis (PsA) is a chronic inflammatory disease that affects approximately 20%‒30% of patients with psoriasis.1 It is characterized by heterogeneous manifestations, including peripheral arthritis, axial involvement, enthesitis, dactylitis, and cutaneous disease.2 PsA can lead to irreversible joint damage, functional disability, and reduced quality of life.3 The complexity of PsA poses significant challenges in comprehensively assessing disease activity, necessitating the use of composite measures that integrate multiple clinical domains.

Among the composite indices developed to assess disease activity in PsA, the Disease Activity Index for Psoriatic Arthritis (DAPSA) has emerged and shown high sensitivity and specificity in distinguishing disease states.4 It incorporates Tender Joint Counts (TJC), Swollen Joint Counts (SJC), Patient Global Assessment (PtGA), Patient Pain Assessment (PtPA), and C-Reactive Protein (CRP), providing a quantitative and clinically feasible assessment of musculoskeletal disease activity.4,5 Previous studies have demonstrated the strong correlation between DAPSA and ultrasound assessments and their predictive value for radiographic progression.6 Furthermore, compared with the complex calculation method of Psoriatic Arthritis Disease Activity Score (PASDAS),7,8 the DAPSA requires only five variables for computation, making it widely applicable in both clinical practice and research settings.9–11

Although DAPSA effectively captures articular involvement, its ability to reflect extra-articular manifestations, particularly the severity of skin disease, remains uncertain. Skin disease severity, typically assessed using the Psoriasis Area and Severity Index (PASI) or Dermatology Life Quality Index (DLQI), may influence PtGA Visual Analogue Scale (VAS) scores12 and CRP,13–17 which are key components of DAPSA. Nevertheless, the extent to which DAPSA indirectly reflects skin disease activity through its various components warrants further investigation.

Therefore, the present study aimed to evaluate whether DAPSA reflects skin disease severity in PsA patients in a Chinese cohort. Specifically, the authors examined the associations between DAPSA and established measures of skin severity (PASI and DLQI) and assessed whether skin involvement affects patient-reported components of the DAPSA score. Understanding this relationship is crucial for interpreting DAPSA scores in patients with prominent skin disease and may inform future approaches to comprehensive PsA assessment.

Musculoskeletal and cutaneous manifestations in PsA are often thought to progress independently,19 making comprehensive disease assessment challenging. Existing tools largely focus on isolated disease domains and may overlook the full clinical spectrum of PsA.10 In the cross-sectional study of 646 Chinese patients with PsA, the authors found that DAPSA, although originally developed for peripheral joint assessment, was significantly associated with skin disease severity. This may be attributed to its inclusion of PtGA, PtPA scores, and CRP levels, which capture elements of systemic inflammation and patient-perceived disease burden. These findings suggest that DAPSA may reflect not only musculoskeletal involvement but also cutaneous manifestations, offering a more holistic measure of PsA disease activity.

The observed increase in PtGA and PtPA scores with worsening PASI supports the hypothesis that skin disease severity contributes to patient-reported outcomes. These findings are aligned with prior studies reporting significant correlations between patient-reported global assessments and PASI,20–22 helping to explain why DAPSA, despite lacking a formal skin domain, can indirectly reflect cutaneous involvement. Moreover, even after matching for musculoskeletal disease activity using PSM, patients with more severe skin involvement exhibited higher DAPSA scores. Notably, patients with severe skin involvement (PASI ≥ 10) had significantly elevated DAPSA scores, global assessments, and CRP levels compared to those with milder skin disease (PASI < 10). These findings underscore the potential role of systemic inflammation, as reflected by elevated CRP, in linking articular and cutaneous manifestations. This association is further supported by previous studies demonstrating that PsA patients with higher CRP levels tend to have more severe skin disease.13–17

Previous studies have demonstrated the validity of DAPSA, showing strong correlations with ACR response and Minimal Disease Activity (MDA), with high sensitivity and specificity (both ≥ 90%), including when compared with joint ultrasonography.5,23–27 The present study is the first to examine the relationship between DAPSA and skin disease severity. The authors observed a weak correlation between DAPSA and PASI, which should be interpreted cautiously. DAPSA should not be considered a substitute for skin assessments, particularly in patients with severe cutaneous involvement. Its practical utility as a holistic screening tool may be best suited for initial global assessment in settings where formal dermatology scoring is unavailable, rather than for precise quantification of skin activity.

Several limitations should be acknowledged. First, the cross-sectional design limits our ability to establish causal relationships between DAPSA and skin disease severity. Second, this study was conducted at a single tertiary center in China, which may limit the generalizability of the present findings to other populations with different genetic, environmental, and clinical characteristics. Thirdly, although the authors applied propensity score matching to adjust for differences in musculoskeletal disease activity, residual confounding due to unmeasured variables ‒ such as psychological burden, treatment adherence, or subclinical inflammation ‒ may still exist. These limitations highlight the need for well-designed prospective studies to clarify the dynamic interplay between skin and joint involvement in PsA and to refine integrated disease activity measures.

Clinically, the present results highlight that DAPSA, although not a substitute for dedicated skin assessments, may serve as a practical and holistic tool for initial disease activity evaluation in PsA, particularly where PASI or DLQI are unavailable. Future research should explore longitudinal relationships between DAPSA and skin severity, and whether integrating PASI into composite indices improves their predictive validity for outcomes like treatment response or radiographic progression.

Qianzi Liu: 0009-0000-8166-6186

Minjia Tan: 0000-0002-8250-8216

Reviewed and approved by Xiangya Hospital (approval nº 2018121106).

This research was funded by the National Key Research and Development Program of China (2023YFC2508105), National Natural Science Foundation of China (82573986, 82373484, 82003354, 82221002, 82130090,82003362).

Qianzi Liu: Methodology; formal analysis; writing-original draft.

Minjia Tan: Conceptualization; data curation; writing-review and editing.

Yehong Kuang: Supervision; funding acquisition; writing, review, and editing.

Qianzi Liu and Minjia Tan share the leading authorship of this manuscript because of their equal and significant contributions to this study.

The entire dataset supporting the results of this study was published in this article.