Generalized pustular psoriasis (GPP) is a rare and severe auto-inflammatory disease characterized by recurrent, sudden, flares of widespread painful erythema and eruption of sterile pustules.^1,2 GPP flares may lead to life-threatening multi-organ complications if left untreated hence rapid and accurate diagnosis is needed.^2,3 However, clinical presentation of GPP is heterogeneous and symptoms may resemble other skin conditions, making accurate and timely diagnosis and treatment challenging.^1,3 As there is a lack of standardized international guidelines for GPP diagnosis, the International Psoriasis Council (IPC) established a Pustular Psoriasis Working Group to address these challenges and develop an international consensus definition and diagnostic criteria for GPP.^1,3

The Pustular Psoriasis Working Group, composed of 8 members from diverse regions, including Malaysia, the United States, Chile, the United Kingdom, Brazil, Japan and France, was thus tasked with developing an international definition and diagnostic criteria for GPP using the modified Delphi method.¹ This involved gathering a set of complex GPP cases which served as the foundation for crafting statements, refining definitions and establishing diagnostic criteria for GPP which involved 2 rounds of virtual consensus meetings with voting to solidify the outcomes.¹

A total of 69 challenging GPP cases from 24 different countries were received and 16 experts were consulted for their opinion on the characteristic features of GPP, features that would exclude GPP as the diagnosis and their favored diagnosis of each case.¹ The working group then curated a comprehensive set of 43 statements that were presented for voting in a 2-round Delphi study and consensus was defined as at least 80% agreement.¹ An expert panel consisting of 25 invited experts and 8 working group members participated in this consensus study.¹

In the initial Delphi round, the group achieved consensus on 51% of the proposed statements, with 22 out of 43 statements receiving at least 80% of the votes.¹ Regarding the key cutaneous features of GPP, the group reached a consensus on the presence of macroscopically visible sterile pustules and scaling.¹ However, erythema was initially rejected, despite it reflecting the inflammatory nature of the condition.¹ After discussion, the group ultimately accepted erythema as an essential feature, acknowledging that it may be difficult to discern in individuals with darker skin tones.¹ Additionally, the group agreed that desquamation, scaling and crusting were indicative of the resolution of pustules, but not mandatory for diagnosing GPP.¹ These accepted statements were then used to shape the proposed definitions and diagnostic criteria for GPP.¹

During the second meeting, 3 definitions were proposed and the definition with the highest number of votes was then revised and unanimously accepted.1 The final recommended definition and essential diagnostic criteria unanimously approved by the group after extensive deliberation are summarized in table 1.

Additionally, the expert panel reached a consensus that while systemic symptoms like fever, fatigue and laboratory abnormalities are not mandatory for diagnosing GPP, their presence can support the diagnosis.¹ The group also highly recommended a skin biopsy, though not mandatory, for confirming the diagnosis and ruling out differential conditions.¹ Furthermore, they advised genetic testing for IL36RN alterations, where available, as these findings may warrant more vigilant monitoring and prioritization for targeted therapies.¹

In conclusion, this international collaborative effort successfully achieved consensus on the definition and diagnostic criteria for GPP using the modified Delphi method.¹ The resulting standardized framework is expected to improve patient care, enhance epidemiological research and lead to a better understanding of the impact of this rare and challenging condition.¹