Development of clinical diagnostic criteria for chronic plaque psoriasis: an international e‐Delphi study

Dear Editor, Despite psoriasis being a common disease, surprisingly little guidance exists on clinical diagnostic criteria.1 The variable presentation of psoriasis and its differential diagnoses make diagnosis challenging,2 particularly for nondermatologists. In 2016, the World Health Organization declared psoriasis a global health concern and highlighted the need to tackle the problem of missed or delayed diagnosis of psoriasis.3 In addition, the UK Psoriasis Association’s priority setting partnership listed the top-10 priority research questions on psoriasis; second on this list was ‘Does treating psoriasis early (or proactively) reduce the severity of the disease, make it more likely to go into remission, or stop other health conditions developing?’4 In order to answer this question, an accurate and timely diagnosis of psoriasis is needed. In response, the Global Psoriasis Atlas, a collaboration between three leading international organizations in world dermatology [International Federation of Psoriasis Associations; International League of Dermatological Societies; and International Psoriasis Council (IPC)] sought to develop clinical diagnostic criteria for chronic plaque psoriasis (CPP) in adults. To address this, three rounds of an e-Delphi consensus survey was undertaken from January to August 2019 to establish diagnostic criteria. Panel members were 50 IPC councillors recruited from 27 countries across six continents, all of whom were consultant dermatologists. After a literature review, 21 potential diagnostic criteria were initially extracted. Using a 9-point Likert scale, participants were asked to rank the importance of the proposed items,5, 6 ranging from ‘extremely unimportant’ to ‘extremely important’. Consensus for inclusion was defined as a median score of ≥ 7 (interquartile range 7–9). Consensus for exclusion and neutral corresponded to median scores of ≤ 3 and 4–6, respectively. Participants were also asked to nominate other diagnostic items that they incorporate into their daily practice when diagnosing psoriasis and to comment on the terminology used in the proposed list of items. Participants were also invited to review a proposed definition of CPP and summary of feedback from each round. Participants were further asked to designate the items that had received a median score of ≥ 7 as either ‘essential’ or ‘supportive’ criteria, and to give their opinions about the number of supportive criteria required to accompany the essential criteria in the final diagnostic dataset. After three rounds of the e-Delphi consensus exercise, the final diagnostic tool consists of a definition of CPP, one essential diagnostic criterion and eight supportive diagnostic criteria (Table 1). Thirty-two panel members agreed that at least four of the eight supportive diagnostic criteria must be present together with the essential criterion to make a diagnosis of CPP. The consensus exercise included a recommendation for the clinical diagnosis of CPP across diverse ethnic groups. The definition of CPP highlighted the most common body sites affected by various clinical variants of psoriasis (e.g. intertriginous and scalp psoriasis). The consensus-developed criteria are intended to standardize psoriasis case definition for epidemiological field studies. This is especially important in helping nondermatologist investigators identify psoriasis, particularly in resource-poor settings, thus facilitating comparison and tracking trends of psoriasis incidence and prevalence in different countries. The diagnostic criteria could also serve as a teaching and training tool for healthcare providers involved in psoriasis management (e.g. nurses, pharmacists and doctors in training), especially in those parts of the world where access to specialist dermatology care is limited. Future research will involve implementing the consensus-agreed diagnostic criteria in an online educational tool supported by illustrations and clinical images to improve the diagnostic abilities of nondermatologists such as general practitioners and other healthcare workers. See Appendix S1 (Supporting Information) for a full list of acknowledgments. Maha Abo-Tabik: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Methodology (equal); Software (equal); Writing-original draft (equal); Writing-review & editing (equal). Rosa Parisi: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing-review & editing (equal). Sarah Willis: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Project administration (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing-review & editing (equal). Christopher Ernest, Maitland Griffiths: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing-review & editing (equal). Darren M. Ashcroft: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing-review & editing (equal). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.