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An international panel of more than 30 experts has developed a consensus definition and diagnostic criteria for generalized pustular psoriasis (GPP).

The new definition, published in , characterized GPP as "a systemic inflammatory disease characterized by cutaneous erythema and macroscopically visible sterile pustules." GPP can occur with or without systemic symptoms, other psoriasis types, and laboratory abnormalities, the panel concluded.

The group also established a key diagnostic criterion for GPP, described as "macroscopically visible sterile pustules on erythematous base and not restricted to the acral region or within psoriatic plaques."

Co-author Peter van de Kerkhof, MD, PhD, is professor of dermatology at Radboud University Nijmegen Medical Centre in The Netherlands, chief medical officer for the International Psoriasis Council. His discussion with the Reading Room has been edited for length and clarity.

Why was there a need or a motivation to develop this consensus definition? To ask it in another way, what was the problem this effort was designed to address?

Van de Kerkhof: The clinical presentation of GPP is quite heterogeneous. You could say that each patient has their own GPP in the sense of several of the presenting signs and symptoms.

Therefore, one can understand that, in looking over the world, there was not a very sharp definition of the clinical phenotype. There has been some heterogeneity among dermatologists on the definition of the presentations of GPP.

There have also been some differences in whether histology is needed. For example, in Japanese guidelines for GPP, histology is very important in confirming the diagnosis. American guidelines suggest that histology may not be needed, that it's important to make a fast diagnosis, and that biopsy and histology only postpone the situation.

Therefore, establishing an internationally accepted standardized definition of GPP based on agreed-upon diagnostic criteria is essential. The aim of this study was to develop an international consensus definition and diagnostic criteria for GPP.

Would you describe the panel of experts convened to develop this definition?

Van de Kerkhof: The International Psoriasis Council established a Pustular Psoriasis Working Group to address the challenges GPP poses. Members of the working group were carefully chosen based on their experience in managing GPP, their involvement in GPP studies, and their publications on GPP. The definition panel included not only dermatologists but experts in the fields of genetics and immunology.

Are there any particular aspects of either the current management of GPP or this consensus definition that you would like to emphasize?

Van de Kerkhof: I think for dermatologists in practice, it's important to realize that GPP is not a frequent condition in many countries.

The essential diagnostic criterion is the presence of visible sterile pustules on an erythematous base -- and this can be with or without other manifestations of psoriasis.

It is important for the practicing dermatologist to realize that this is not exclusively a psoriasis-related condition. It can occur in patients without any signs of symptoms of psoriasis and who will never develop psoriasis, but they have GPP.

The essential criteria here are the pustules and the erythema, with supporting diagnostic criteria being fever, fatigue, and various lab abnormalities. These are not mandatory; you can have GPP without any of these supporting criteria. When you see a patient with generalized pustules and erythema, consider a GPP diagnosis.

What, if any, are the next steps in this process? What does the panel hope will change or occur in the foreseeable future for GPP care as a result of the new definition and criteria?

Van de Kerkhof: In addition to having a clinical impact, we hope this work will be used as a sort of document for education. Based on adequate education we will start to better diagnose GPP.

It is our impression that a lot of patients with GPP receive an ill-defined diagnosis, maybe of pustular disease, where people in intensive care units often think patients with GPP may have had sepsis. What we hope is that these simple and very informative criteria help patients get a better diagnosis.

We also hope to find a good compromise between the Japanese and the American view related to the biopsy. That is, the group feels that a biopsy gives very important information, but it is important not to wait for a few days to start a treatment. On one hand, a biopsy provides a better, more precise diagnosis, but not for the immediate diagnosis. For the immediate diagnosis, we recommend a fast approach to diagnosis and treatment. Better care is what we hope for.

Is there anything else you would like to communicate?

Van de Kerkhof: It's important to realize that the treatment of generalized pustular psoriasis in the past was derived from experience in the treatment of psoriasis in general. It was a question of trial and error to find the most optimal treatment.

It's very important also now that a biologic, spesolimab, has become available recently in many countries. This drug targets IL-36 signaling and provides new opportunities for the treatment of flares in patients with GPP.