Abstract
Background
The emergence of new treatments has significantly elevated treatment expectations for psoriasis. However, existing Korean severity definitions and treatment targets of psoriasis remain primarily centered on traditional Psoriasis Area and Severity Index (PASI) and Body Surface Area (BSA) thresholds, often underestimating the disease burden in high-impact special areas.
Objective
To develop a revised Korean expert consensus on psoriasis severity and treatment targets that incorporate the clinical significance of special areas and reflect the evolving therapeutic landscape.
Methods
A modified Delphi method was employed involving a panel of 65 dermatologists specializing in psoriasis from universities and training hospitals across South Korea. Two rounds of anonymous web-based surveys were conducted.
Results
A strong consensus was achieved on a new definition of moderate-to-severe psoriasis: (1) PASI ≥10, or (2) 5< PASI <10 with concomitant special area involvement (defined as ≥30% affected surface area of the specific site and a static Physician’s Global Assessment (sPGA) score ≥3). For treatment targets, the panel established ‘Absolute PASI ≤2’ as the primary realistic goal. Site-specific goals were defined for special areas, to achieve an affected surface area <10% or an sPGA of 0/1. The Dermatology Life Quality Index was excluded from the mandatory severity definition or treatment target to preserve objectivity and feasibility in high-volume clinical settings.
Conclusion
This consensus provides a practical and objective framework for managing psoriasis in Korea. These recommendations provide quantifiable criteria and stringent targets to optimize clinical decisions and patient outcomes in the era of advanced therapeutics.
Keywords: Clinical decision-making, Consensus, Delphi method, Psoriasis, Severity of illness index, Treatment outcome
INTRODUCTION
Psoriasis is a chronic inflammatory skin disease characterized by erythematous plaques with silvery scales, affecting 60 million people worldwide1. Psoriasis has a high prevalence and is associated with various comorbidities, including obesity, metabolic syndromes, cardiovascular diseases, and mental health disorders2,3,4,5. Considering the prevalence, comorbidities, and the emergence of expensive new treatments, such as biologics and small molecule drugs, psoriasis imposes a substantial economic burden on both individuals and society compared to other skin diseases2. This economic burden has driven significant research and development efforts, leading to substantial advancements in psoriasis treatment, particularly with the introduction of biologics in the 2000s and 2010s6.
Before the widespread use of biologics, treatment goals for psoriasis were often focused on reducing symptoms and improving quality of life. However, with the advent of these highly effective therapies, treatment targets have been progressively elevated, with 75% reduction in Psoriasis Area and Severity Index (PASI 75), PASI 90, and even complete clearance becoming achievable goals7,8,9. Despite these advances, complete clearance (PASI 100) remains difficult to achieve in routine clinical practice, particularly in patients with involvement of high impact areas. Consequently, recent guidelines emphasize the need for intensive treatment of psoriasis affecting special areas, such as the scalp, palmoplantar areas, inverse areas (intertriginous areas like the axillae, groin, and inframammary folds), genital psoriasis, and nail psoriasis, as these locations often present significant challenges in achieving complete remission. In parallel with these developments, recent guidelines and expert consensus statements demonstrate a growing trend towards including 'special areas' in the assessment and definition of psoriasis severity10,11,12,13.
However, the current Korean definitions rely predominantly on PASI and Body Surface Area (BSA) thresholds, with limited consideration of disease burden in special areas. Consequently, we undertook this study to develop a revised Korean expert consensus on psoriasis severity and treatment targets using a modified Delphi method.
MATERIALS AND METHODS
The Consensus Statements Development Working Group, representing the Korean Society for Psoriasis, consisted of seven core members who conducted a systematic review of the literature and oversaw the development of the consensus statements. The working group invited 110 experts to form the panel, comprising executives and councilors of the Korean Society for Psoriasis, as well as dermatologists from universities and training hospitals nationwide who explicitly list psoriasis as a clinical specialty on their institutional websites. Among the 110 expert panel members, 65 participated and completed both rounds of the questionnaire survey. The panel characteristics are presented in Table 1.
Table 1. Characteristics of the Delphi panel.
| Characteristics | Delphi panel (n=65) | |
|---|---|---|
| Sex | ||
| Male | 41 (63.1) | |
| Female | 24 (36.9) | |
| Age (yr) | 50.4±10.1 | |
| Age distribution | ||
| 30–39 | 6 (9.2) | |
| 40–49 | 31 (47.7) | |
| 50–59 | 16 (24.6) | |
| 60–69 | 9 (13.8) | |
| ≥70 | 3 (4.6) | |
| Type of practice | ||
| Hospital-based practice | 62 (95.4) | |
| Private clinic-based practice | 3 (4.6) | |
Values are presented as mean ± standard deviation or number (%).
Literature review
We conducted a systematic literature review to identify definitions of psoriasis severity and treatment targets. A search of MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials was performed on September 18, 2023, for full-text studies published between 2013 and September 2023. The search utilized terms including “psoriasis,” “plaque psoriasis,” “psoriasis assessment,” “psoriasis index,” “psoriasis measurement,” “psoriasis scale,” “consensus,” and “guideline.” A total of 48,227 articles related to psoriasis were initially identified, after removing duplicates and screening titles and abstracts, 331 were reviewed. Finally, 23 key articles were ultimately selected to develop the items for the Delphi rounds.
Consensus process
A modified Delphi method comprising two rounds of web-based questionnaires (Google Form) was adopted for the consensus process. The survey was conducted anonymously to prevent dominance by specific individuals. In round 1, panelists evaluated the need for a comprehensive update and the establishment of a new guideline regarding psoriasis treatment targets, in light of recent international revisions and current Korean standards. In round 2, panelists were asked to provide their opinions on whether they agreed with the proposed definition of psoriasis severity and the treatment target. The panelists scored their level of agreement for each statement using a ten-point scale ranging from 1 to 10 (1–3, disagree; 4–6, neutral; 7–10; agree). The participants provided queries and comments in free text as feedback in both rounds. The criteria for consensus were predefined based on the methodology established in the previous Korean expert consensus for plaque psoriasis9. Specifically, consensus was achieved if more than 70% (>70%) of participants provided a score of ≥7 for a statement. Strong consensus was achieved if more than 80% (>80%) of participants provided a score of ≥7 for a statement.
RESULTS
The definition of psoriasis severity
1) Outcomes of the round 1 Delphi survey
The survey items, mean agreement scores, and agreement rates from the first round are summarized in Fig. 1. Regarding existing definitions, the recategorization proposed by the International Psoriasis Council (IPC) in 2020 achieved the highest consensus (agreement rate 90.8%)10, followed by the 2018 Asian consensus (86.2%)14. In contrast, the European consensus definition failed to meet the consensus criteria (66.2%)7.
Fig. 1. Results of the round 1 Delphi survey for establishing a Korean consensus on the definition of psoriasis severity.
PASI: Psoriasis Area and Severity Index, BSA: Body Surface Area, PGA: Physician’s Global Assessment, DLQI: Dermatology Life Quality Index.
For the revised definition from Spanish group13, strong consensus was achieved on defining moderate-to-severe psoriasis based on quantitative scores (PASI >10, BSA >10, or Dermatology Life Quality Index [DLQI] >10) and the requirement for systemic treatment (both 89.2%). The inclusion of functional or psychological impact due to special area involvement also reached a strong consensus (86.2%).
In terms of clinical applicability, the panel demonstrated strong consensus on PASI (87.7%) and BSA (87.7%), as well as static Physician’s Global Assessment (sPGA) (83.1%), for real-world practice. However, the applicability of DLQI did not reach consensus, nor did the proposal to add a 'minimal severity' category (47.7%). On this basis, PASI (84.6%) and BSA (75.4%) were identified as the essential components for the new definition (Supplementary Fig. 1A).
Regarding special areas, there was strong consensus to determine overall severity by incorporating the extent of involvement at these sites (86.2%) and using sPGA-based criteria (sPGA 3 for moderate, 4 for severe; 90.8%). A majority of respondents (56.9%) identified 30% involvement as the appropriate cutoff to distinguish mild from moderate-to-severe psoriasis (Supplementary Fig. 1B).
2) Outcomes of the round 2 Delphi survey
A second round was conducted to refine index selection and reclassification criteria (Fig. 2). The panel reached a strong consensus on excluding DLQI from the severity definition (83.3%) and adopting a single index (PASI or BSA) as the sole criterion (80.3%). Specifically, experts reached consensus on preferring PASI over BSA (75.8%), whereas the preference for BSA did not meet the threshold (56.1%). The addition of sPGA as a supplementary criterion was also rejected for both PASI and BSA thresholds.
Fig. 2. Results of the round 2 Delphi survey regarding the selection of severity indices and criteria for special area reclassification.
DLQI: Dermatology Life Quality Index, PASI: Psoriasis Area and Severity Index, BSA: Body Surface Area, PGA: Physician’s Global Assessment.
The panel established criteria for reclassifying mild psoriasis to moderate-to-severe in patients with special area involvement. Although applying “either criterion” (area or sPGA) reached consensus (72.7%), applying “both criteria” (≥30% involvement and sPGA ≥3) was selected as it achieved strong consensus (80.3%).
Regarding specific thresholds for reclassification, the majority selected the range of 5< PASI <10 (59.1%) (Supplementary Fig. 1C). Based on these results, the final definition of moderate-to-severe psoriasis was determined as follows: 1) a PASI score ≥10, or 2) a PASI score between 5 and 10 with concomitant special area involvement (affected surface area ≥30% and sPGA ≥3).
Treatment target of psoriasis
1) Outcomes of the round 1 Delphi survey
Fig. 3 summarizes the survey items, mean agreement scores, and agreement rates regarding treatment targets for psoriasis from the first round. The 2011 treatment goals by Mrowietz et al.7, which served as the foundation for the current National Health Insurance Criteria for moderate-to-severe psoriasis, showed a mean agreement score of 6.6 and an agreement rate of 63.1%, indicating a need for revision. The expert panel reached a strong consensus on the definition of ‘good response’ based on the 2021 Italian consensus15. Specifically, achieving Absolute PASI ≤3 or sPGA 0/1 (92.3% agreement) and reaching ΔPASI ≥90 (93.8% agreement) were identified as primary treatment goals with a strong consensus. In contrast, the inclusion of DLQI <5 as a criterion for patients achieving only a ΔPASI 75–90 failed to achieve consensus (67.7%). Notably, a strong consensus was reached that, even when systemic criteria are met, defining an adequate treatment goal requires achieving a sPGA of 0/1 (clear/almost clear) in special areas if residual lesions persist.
Fig. 3. Results of the round 1 Delphi survey for establishing a Korean consensus on the treatment target of psoriasis.
PASI: Psoriasis Area and Severity Index, PGA: Physician’s Global Assessment, DLQI: Dermatology Life Quality Index, BSA: Body Surface Area, PSSI: Psoriasis Scalp Severity Index, NAPSI: Nail Psoriasis Severity Index.
In establishing goals tailored to the Korean clinical setting, the panel reached a strong consensus (96.9%) on the necessity of distinguishing between ‘ideal’ and ‘realistic’ treatment targets. For the realistic treatment target, a strong consensus (95.4%) supported adopting PASI 90 as the appropriate standard, whereas PASI 100 did not achieve consensus (55.4%). When considering the type of indicator, 84.6% of the panel preferred absolute scores (e.g., absolute PASI) to relative response rates (e.g., PASI 90/100) as a realistic treatment target.
While various guidelines have proposed treatment targets of PASI ≤2 or ≤3, the 2020 British Association of Dermatologists recommendations, which adopt PASI ≤2, have significantly influenced global standards16. We investigated the clinical preference between PASI ≤2 and PASI ≤3 within the Korean context. Overall, 81.5% of experts considered absolute PASI ≤2 to be more appropriate than absolute PASI ≤3 (Supplementary Fig. 2A), a view supported by an 89.2% agreement rate in the statement survey. As a result, absolute PASI ≤2 was selected as the most suitable treatment target indicator for the Korean medical environment among all proposed criteria.
For special areas, there was a strong consensus that achieving a sPGA of 0/1 was the most critical treatment target, consistently outperforming other auxiliary metrics such as surface area or Nail Psoriasis Severity Index (NAPSI) scores. The agreement rates indicated a strong consensus across all specific sites: Scalp sPGA 0/1 (95.4%), sPGA 0/1 for inverse psoriasis (95.4%), and Nail sPGA 0/1 (90.8%).
2) Outcomes of the round 2 Delphi survey
Following the first round of the Delphi process, concerns were raised about practical difficulties in clinical settings when various criteria are used as treatment targets. Round 2 of the Delphi survey was conducted to determine whether to include multiple-criteria treatment target definitions or to select only one.
The results indicated that the majority of respondents (66.2%) preferred including only one criterion, while 33.8% favored including multiple criteria (Supplementary Fig. 2B). Given that ‘absolute PASI ≤2’ had already achieved strong consensus as the treatment target in the first round of the Delphi process, it was selected as the sole primary criterion. The final treatment targets were defined as follows: the primary goal is achieving an absolute PASI ≤2. When psoriasis involves special body areas, the target is defined as reaching an affected surface area of <10% or a sPGA score of 0 or 1. For nail psoriasis, achieving a NAPSI score of 75 was set as the specific goal.
DISCUSSION
This study developed a consensus on the definition of psoriasis severity and treatment targets relevant to the Korean clinical setting using a modified Delphi approach. Through this process, the expert panel integrated international recommendations and guidelines with real-world clinical practice in Korea and proposed revised criteria for disease severity and treatment target of psoriasis. The final consensus statements are summarized in Table 2.
Table 2. Summary of the final consensus on the definition of psoriasis severity and treatment targets.
| Category | Consensus definition | |
|---|---|---|
| Definition of moderate-to-severe psoriasis | ||
| Primary criteria | PASI score ≥10 | |
| Conditional criteria (with special area involvement) | 5< PASI score <10 with affected surface area (special site) ≥30% AND sPGA ≥3 | |
| Realistic treatment targets | ||
| Primary goal | Absolute PASI ≤2 | |
| Special areas | Affected surface area <10% OR sPGA 0/1 | |
| Nail psoriasis | NAPSI 75 OR sPGA 0/1 | |
PASI: Psoriasis Area and Severity Index, sPGA: static Physician’s Global Assessment, NAPSI: Nail Psoriasis Severity Index.
Regarding the definition of psoriasis severity, our new consensus is unique in establishing criteria to escalate mild psoriasis to moderate-to-severe psoriasis. Although numerous contemporary guidelines emphasize that involvement of special areas warrants systemic treatment, there remains a notable absence of clear, objective criteria to quantify the severity of disease at these specific sites (affected surface area ≥30% and sPGA ≥3)10,11,12,13. To address this gap, the Korean expert panel reached a consensus on quantifiable thresholds for disease severity escalation, specifically by integrating the affected surface area and sPGA scores for each special site. This approach is particularly relevant in Korea, where the National Health Insurance Service functions as a single-payer system and reimbursement decisions are based on predefined objective clinical criteria17. Accordingly, the use of quantifiable assessment scores is necessary to support consistent disease monitoring and to facilitate appropriate access to advanced therapies.
Another important outcome of this consensus process was the introduction of a conditional severity category. The panel agreed that patients with lower PASI scores (5–10) may be reclassified as having moderate-to-severe disease when there is clinically meaningful involvement of special or high-impact areas. This approach reflects recognized limitations of PASI-based assessment, which prioritizes overall disease extent and may therefore underestimate disease burden in patients with localized but functionally or psychosocially significant lesions18,19.
In contrast, the DLQI was not included as a mandatory component of the severity definition. As a patient-reported outcome (PRO) measure, the DLQI reflects subjective perceptions of disease impact and may be influenced by individual response patterns and contextual factors. In addition, routine administration of questionnaire-based instruments can be challenging in high-volume outpatient settings, particularly in healthcare systems such as that of South Korea, where outpatient visit volumes are high and consultation times are relatively limited20. Excluding the DLQI from the mandatory definition was therefore intended to reduce variability related to subjective reporting and to preserve a primarily clinician-based, objective framework for severity classification21,22. The panel also noted that the development of alternative PRO measures to replace the DLQI, and their eventual integration into severity definitions, remains an important issue for future research and consensus building.
Regarding the treatment target of psoriasis, this study is unique in that it captures, through expert consensus, a shift toward stricter treatment targets made possible by advances in biologic therapy. The expert panel identified absolute PASI ≤2 as the most suitable realistic treatment target. This standard is more stringent than previous treatment targets used in Korean clinical practice and prior domestic consensus statements, which generally defined treatment failure as failure to achieve PASI 759. This new treatment target is consistent with the NPF Treat-to-Target strategy (BSA ≤1%) and is more strict than the absolute PASI ≤3 thresholds recommended in the 2023 Australian and 2021 Italian guidelines12,15,23. Although the state of “clear or almost clear” skin can be assessed using the sPGA and has been shown to correlate well with an absolute PASI ≤216, absolute PASI provides a more quantitative and objective measure and the preference for absolute PASI in this consensus likely reflects the tendency of Korean experts to favor objective, reproducible severity indices when defining treatment targets. Furthermore, an emphasis on efficiency among Korean experts may have influenced the selection of absolute PASI ≤2 as the sole treatment target, without including additional parallel criteria. This pattern is also observed in the proposed definition of psoriasis severity.
This consensus is also characterized by the inclusion of quantitative treatment targets for special areas. Existing guidelines, such as the IPC recategorization, primarily utilize special area involvement as a criterion for defining severity or initiating systemic therapy but rarely establish specific therapeutic endpoints15,24. Real-world data from Korea have shown that a substantial proportion of patients exhibit biologics-resistant disease in body regions traditionally considered difficult to treat, including the fingernails (10.0%), toenails (14.0%), scalp (38.0%), palms (12.0%), soles (14.0%), and genital areas (10.0%)25. Even among patients achieving a good overall treatment response, residual psoriasis in these special areas was frequently observed, and in the absence of clear, site-specific treatment targets, such residual disease has often been overlooked in routine clinical practice. To address this unmet need, our consensus specifies site-specific treatment goals, including sPGA 0/1 for scalp and inverse psoriasis and NAPSI 75 for nail psoriasis, suggesting that improvement in overall PASI alone may fail to address clinically relevant residual disease persists in high impact areas21,24,26. For nail psoriasis, NAPSI 75 was included as an additional criterion, reflecting the clinical reality that nail involvement is generally more difficult to treat and responds more slowly to therapy compared with other manifestations of psoriasis27. Although concerns were raised regarding the time required for NAPSI assessment and the potential need for alternative criteria, its selection also took into account that it remains the most readily available and objective quantitative measure in current clinical practice28. These new treatment targets for special areas may encourage clinicians to pay closer attention to residual disease in difficult-to-treat areas.
An additional strength of this consensus is the definition of realistic treatment targets, which reflects the limited proportion of experts who considered complete clearance a feasible goal in everyday practice. While the panel acknowledged PASI 100 as the ideal goal, adopting absolute PASI ≤2 as a realistic target provides a balanced framework for clinical decision-making. In the current era of biologics and advanced small molecule drugs, this consensus may provide a balanced clinical framework that prevents premature or excessive therapeutic switching while simultaneously reducing the patient burden associated with suboptimal outcomes, thereby motivating dermatologists to strive for the high levels of clearance now achievable with current therapies16,29,30.
This study has several limitations. As a Delphi-based study, the results rely on expert opinion rather than direct clinical trial data. There may be a discrepancy between these consensus recommendations and the current strict reimbursement criteria of the Korean National Health Insurance system.
In summary, this consensus proposes a practical framework for defining psoriasis severity and treatment targets in the Korean clinical setting by incorporating objective, quantifiable criteria and site-specific considerations. By addressing limitations of traditional PASI-based assessment and emphasizing realistic yet stringent treatment goals aligned with modern therapies, these recommendations may support more consistent clinical decision-making and improved patient-centered outcomes, while also serving as a reference for future guideline development and policy discussions.
ACKNOWLEDGMENT
We express our sincere appreciation to all dermatologists who contributed to the development of this expert consensus, with special recognition of those who actively served as members of the steering committee.
Footnotes
FUNDING SOURCE: This work was supported by the Korean Society for Psoriasis.
CONFLICTS OF INTEREST: The authors have nothing to disclose.
DATA SHARING STATEMENT: The data that support the findings of this study are available from the corresponding authors upon reasonable request.
SUPPLEMENTARY MATERIALS
Results from the survey regarding the Korean consensus on psoriasis severity definitions. (A) Essential assessment tools identified for inclusion in the definition of psoriasis severity. (B) Preferred threshold for the extent of involvement in special areas to distinguish mild from moderate-to-severe psoriasis. The majority of respondents (56.9%) selected 30% involvement as the appropriate cutoff. (C) Expert consensus on the PASI range for severity reclassification. Regarding the PASI score, 59.1% of experts agreed that the range of 5< PASI <10 is the appropriate threshold for severity reclassification.
Results from the survey regarding the Korean consensus on the treatment target of psoriasis. (A) Expert consensus on the preference for absolute PASI ≤2 over absolute PASI ≤3. When asked to select the most appropriate treatment target threshold for the Korean clinical setting, 81.5% of experts selected absolute PASI ≤2, whereas 18.5% selected absolute PASI ≤3 (n=65). (B) Preference for single vs. multiple criteria. The pie chart illustrates the percentage of respondents who favored including a single criterion (66.2%) vs. those who supported multiple criteria (33.8%) in the treatment target definition.
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Associated Data
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Supplementary Materials
Results from the survey regarding the Korean consensus on psoriasis severity definitions. (A) Essential assessment tools identified for inclusion in the definition of psoriasis severity. (B) Preferred threshold for the extent of involvement in special areas to distinguish mild from moderate-to-severe psoriasis. The majority of respondents (56.9%) selected 30% involvement as the appropriate cutoff. (C) Expert consensus on the PASI range for severity reclassification. Regarding the PASI score, 59.1% of experts agreed that the range of 5< PASI <10 is the appropriate threshold for severity reclassification.
Results from the survey regarding the Korean consensus on the treatment target of psoriasis. (A) Expert consensus on the preference for absolute PASI ≤2 over absolute PASI ≤3. When asked to select the most appropriate treatment target threshold for the Korean clinical setting, 81.5% of experts selected absolute PASI ≤2, whereas 18.5% selected absolute PASI ≤3 (n=65). (B) Preference for single vs. multiple criteria. The pie chart illustrates the percentage of respondents who favored including a single criterion (66.2%) vs. those who supported multiple criteria (33.8%) in the treatment target definition.