Table 1.

Features of pustular psoriasis variants and acute generalized exanthematous pustulosis.

Disease	Clinical Morphology	Demographic	Pathology	Treatment
Generalized pustular psoriasis (GPP)	All PP subtypes contain sterile pustules [3]. Disseminated, painful erythematous lesions covered with aseptic pustules [3,8]. Severe systemic symptoms, including fever, malaise, fatigue, and arthritis, may be present [3,4].	Fifth decade of life with slight female predominance [4].	Pathogenesis: Disruption of the interleukin-36 pathway plays a major role (mutations in IL36RN), although there is significant heterogeneity in the gene pathways implicated [3,9,10]. The innate immune system, environmental factors, and genetic susceptibility all contribute [7]. Histopathology: Spongiform pustules of Kogoj in the epidermis and microabscesses of Munro [3,4]. Parakeratosis and psoriasiform hyperplasia [8].	Topical corticosteroids, oral retinoids (i.e., acitretin), cyclosporine, methotrexate, TNF-α inhibitors (i.e., adalimumab), anti-IL-17 monoclonal antibody (i.e., secukinumab), anti-IL-23 monoclonal antibody (i.e., guselkumab), anti-IL-1β monoclonal antibodies (i.e., gevokizumab and canakinumab), IL-1R inhibitor (i.e., anakinra), PDE-4 inhibitor (i.e., apremilast) [3,4,7,9,11,12,13,14].
Impetigo herpetiformis	All PP subtypes contain sterile pustules [3]. See GPP.	GPP during third trimester of pregnancy [3].	Pathogenesis: see GPP. Histopathology: see GPP.	Cyclosporine, systemic corticosteroids [3,4]
Palmoplantar pustular psoriasis (PPPP)	All PP subtypes contain sterile pustules [3]. Pustules intermixed with yellow-brown macules on palms and soles [7,8,15].	Slight female predominance [4,5]	Pathogenesis: Mutations in IL36RN make up a significantly smaller proportion of cases compared to GPP [4,5]. Mutations in AP1S3 and CARD14, as well as abnormalities of eccrine sweat glands, have been implicated in PPPP [7]. Histopathology: see GPP; on acral skin.	See GPP.
Acrodermatitis continua of Hallopeau	All PP subtypes contain sterile pustules [3]. Pustular lesions overlying erythematous, scaling skin on the tips of the fingers and toes [3,4,8].	Slight female predominance [4,5].	Pathogenesis: see GPP. Histopathology: see GPP, on acral skin.	Topical corticosteroids, calcipotriene [3,4]
Annular pustular psoriasis	All PP subtypes contain sterile pustules [3]. Pustules located circumferentially on erythematous skin lesions. Lesions present on limbs, buttocks, abdomen. Can present with fever and malaise [16].	More common in children [16].	Pathogenesis: see GPP. Histopathology: see GPP.	See GPP.
Acute generalized exanthematous pustulosis	Sterile, pin-sized pustules overlying edematous and erythematous skin. Often appears on the face or intertriginous areas before spreading to the trunk and limbs [17]. Acutely accompanied by fever, neutrophilia, and eosinophilia [18].	More common in adults with a slight female predominance [17].	Pathogenesis: Drug-specific T-cell predominantly infiltrates with neutrophil accumulation mediated by IL-8 and GM-CSF [19,20,21]. Th17 cells are also involved in neutrophil activation [21]. Mutations in IL36RN found in some patients [20]. Histopathology: Spongiform subcorneal or intraepidermal pustules ± necrotic keratinocytes, vacuolar interface dermatitis, dermal eosinophilia, psoriasiform hyperplasia [17,22].	Typically resolves within 2 weeks of discontinuation of the offending drug [20,23]. Topical steroids are often used for symptomatic relief [20]. Systemic corticosteroids or cyclosporine are useful in severe cases or with extracutaneous involvement [24,25].

GPP: generalized pustular psoriasis; PP: pustular psoriasis; PPPP: palmoplantar pustular psoriasis.