Diagnosing generalised pustular psoriasis

Generalised pustular psoriasis (GPP) is a potentially life-threatening disease, which, until recently, had no clear guidance for diagnosis. At IFPA 2024, Dr Siew Eng Choon (Monash University Malaysia, Malaysia) presented the 2024 guidance for the diagnosis of GPP and described the differential diagnosis between GPP and other conditions that can present similarly [1].

According to the new guidelines from the International Psoriasis Council, GPP should be defined as “a systemic disease characterised by cutaneous erythema and macroscopically visible sterile pustules” with the following subclassifiers:

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  • manifesting with or without systemic symptoms and signs;
  • may or may not manifest with other types of psoriasis;
  • can present as an acute form with widespread pustular eruption or a subacute variant with annular phenotype; and
  • laboratory anomalies may or may not be present [2].

Essential diagnostic criteria for GPP include macroscopically sterile pustules on an erythematous base not restricted to the acral region or within psoriatic plaques. Supporting diagnostic criteria can include lakes of pus, painful skin, fatigue, fever, history of recurring flares, family history of psoriasis, elevated CRP, leukocytosis, neutrophilia, abnormal laboratory findings (i.e. hypocalcaemia, hyponatraemia, hypoalbuminaemia, abnormal renal or liver function tests), spongiform pustules of Kogoj on biopsy confirmation, and positive genetic findings (i.e. IL36RN mutation, MPO, AP1S3, SERPINA, CARD14).

Differential diagnosis

Psoriasis with pustules should not be classified as GPP. Acral pustules can present during flares and should not rule out GPP diagnoses; however, pustules that present only on acral lesions should not be classified as GPP.

GPP diagnosis should be distinguished from conditions such as acute generalised exanthematous pustulosis, pemphigus foliaceus, IgA pemphigus, and subcorneal pustular dermatosis [1]. Acute generalised exanthematous pustulosis presents following administration of medications, most commonly penicillins with numerous pin-point discrete sterile pustules, while GPP presents with widespread sterile pustules and lakes of pus. Facial pustular lesions occur commonly in acute generalised exanthematous pustulosis, while acral lesions are very rare. Finally, another distinguishing feature between acute generalised exanthematous pustulosis and GPP is the speed of onset and resolution: acute generalised exanthematous pustulosis has a rapid onset and resolution and does not relapse, while GPP flares can take 3 to 5 weeks and relapse.

Subcorneal pustular dermatosis presents with flaccid sterile pustules, which are absent in GPP, and does not present with facial and acral lesions. Another distinguishing feature is spongiosis, which is absent in subcorneal pustular dermatosis. Pemphigus foliaceus and IgA pemphigus can present similarly to GPP but histology and direct and indirect immunofluorescence (IgA deposits) can distinguish these diseases.

“GPP is a potentially life-threatening disease systemic inflammatory disease characterised by cutaneous erythema and macroscopically visible sterile pustule,” said Dr Choon. “The new International Psoriasis Council consensus on the definition and diagnostic criteria for GPP provides a clear and standardised framework for diagnosis.”

1. 
   
   1. Choon SE. Generalized pustular psoriasis: Definition and challenges. IFPA Conference 2024, 27–29 June, Stockholm, Sweden.
   2. Choon SE, et al. JAMA Dermatol. 2024. DOI:10.1001/jamadermatol.2024.0915.

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Posted on 17 July 202417 July 2024