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An international consensus statement on generalized pustular psoriasis (GPP) from the International Psoriasis Council (IPC) includes the recommendation that considerations such as body surface area (BSA) affected and duration of pustulation are not essential when diagnosing GPP, to speed clinical decisions without sacrificing accuracy, according to the statement's authors.

The consensus is the result of a working group established by the IPC, made up of international experts in GPP, which developed an international definition and diagnostic criteria for GPP that was published in JAMA Dermatology on May 1 and highlighted on the IPC website on May 2.

"Without an internationally accepted definition and diagnostic criteria," corresponding author Siew Eng Choon, MBBS, told this news organization, "the rarity and heterogenous nature of GPP, along with its similarity to other pustular dermatoses, often lead to delayed diagnoses and potential misdiagnoses."

Delayed and erroneous diagnoses can increase the risk for severe GPP complications, such as sepsis and organ failure, leading to poor patient outcomes and potentially fatal consequences, added Choon, associate professor, Monash University Malaysia, and senior consultant in dermatology, Hospital Sultanah Aminah, Johor Bahru, Malaysia.

Along with facilitating comparative and cross-regional research, wrote Choon and colleagues, having unified, precise criteria to drive timely GPP diagnoses becomes especially important with the approval of an effective targeted treatment for GPP. (In September 2022, the US Food and Drug Administration approved the interleukin [IL]-36 antagonist spesolimab for the treatment of flares associated with GPP in adults, which was recently expanded to include children aged 12 years and older.)

Case-Based Approach

To answer questions such as which clinical features are necessary or unnecessary for a GPP diagnosis, a 33-member panel (including eight members of the IPC's Pustular Psoriasis Working Group) crafted 43 statements based on expert analysis of 64 challenging GPP cases. Using a two-round Delphi process that required at least 80% agreement, the panel approved 23 consensus statements, encapsulated in the following items:

• Definition: "GPP is a systemic inflammatory disease characterized by cutaneous erythema and macroscopically visible sterile pustules."
• Essential diagnostic criteria: Macroscopically visible sterile pustules on an erythematous base "and not restricted to the acral region or within psoriatic plaques."

Initially, panelists disagreed regarding the importance of erythema because of the difficulty of appreciating redness in darker skin. But ultimately, they deemed this indicator of GPP's inflammatory nature as essential as pustules, which signify the condition's neutrophilic aspect.

The proposed criteria differ from existing GPP guidelines in important ways. For example, Japanese guidelines published in The Journal of Dermatology in 2018 require recurrence, biopsy confirmation, and systemic features for a definitive diagnosis. A European consensus statement published in the Journal of the European Academy of Dermatology and Venereology in 2017 limits the presence of sterile pustules to non-acral skin, with relapse or persistence beyond 3 months, with or without systemic inflammation.

"We unanimously agreed that pustular lesions on acral regions may be present during flares and should not rule out a diagnosis of GPP," Choon said in the interview.

The authors moreover deemed pustular duration nonessential for diagnosis. "GPP is a life-threatening disease," they wrote. "Therefore, diagnosis should not be delayed by any predefined duration of pustulation or BSA." Supporting elements such as lakes of pus, fatigue, fever, and painful skin may occur with GPP, they added, but are not diagnostic.

Clinical Consistency

When dermatologists suspect GPP, Choon recommended following a systematic approach guided by the proposed diagnostic criteria. "First, conducting a comprehensive patient history is paramount." Investigating recent drug exposures can rule out the most challenging differential diagnosis, acute generalized exanthematous pustulosis (AGEP), she said.

Assessing personal or family history of psoriasis and previous pustular flares can support a GPP diagnosis. Next, Choon suggested thoroughly examining pustular morphology and distribution and performing laboratory tests.

If diagnostic criteria are not met, the panel strongly recommended a biopsy to rule out GPP mimics. "Specifically," said Choon, "discrete pinpoint pustules without coalescence should raise suspicion for AGEP, while hypopyon pustules suggest subcorneal pustular dermatosis." Biopsy recommendation notwithstanding, she added, the clinical presentation of classic GPP is often distinctive enough to warrant immediate treatment initiation without awaiting biopsy results. The panel also recommended screening for IL36RN mutations, if available.

"Overall," Choon said, "adhering to the proposed diagnostic criteria ensures a standardized, comprehensive approach in the evaluation and management of suspected GPP cases, thereby facilitating accurate diagnosis and appropriate treatment."

The study was funded by the IPC. Choon received personal fees from AbbVie, Almirall, Boehringer Ingelheim, Lilly, Janssen Pharmaceuticals, Novartis, Pfizer, Sanofi, and UCB outside of the study. The other authors had multiple disclosures listed.

John Jesitus is a Denver-based freelance medical writer and editor.