Generalized pustular psoriasis (GPP) is a rare and severe form of psoriasis that presents as a widespread eruption of sterile superficial pustules with background erythema, with or without systemic inflammation. Pustular psoriasis, particularly in the acute setting, can be a severe inflammatory disease that requires hospitalization and aggressive therapy. Untreated disease can also progress to erythroderma.

There are 3 subtypes of GPP:

• von Zumbusch type (GPP) – Acute onset of generalized erythema and pustules with systemic manifestations including fever, skin tenderness, malaise, arthralgias, headache, and nausea. After several days, the pustules resolve to become confluent, scaling plaques.
• Exanthematic type – Acute onset of small pustules that are triggered by an infection or a drug. This subtype usually lacks systemic symptoms.
• Annular subtype – Erythematous, annular lesions that have pustules at the advancing edge of a lesion and is associated with fever, malaise, and other systemic manifestations. The annular variant is the most common form of pustular psoriasis in children.

Although GPP can affect any age group, it is most commonly seen in adults aged 40-50 years, with a higher percentage of women affected. Approximately 50% of pregnant patients with psoriasis report improvement of disease burden. However, there are many reports that show the development of pustular psoriasis in pregnant patients who are hypocalcemic. Pustular psoriasis that occurs during pregnancy is termed impetigo herpetiformis. This represents a risk to both maternal and fetal health (including risk of stillbirth) and should be treated aggressively.

GPP can also present in infants and children, and these patients may have a known genetic mutation. Genetic associations involving interleukin-36 receptor antagonist (IL36RN); the keratinocyte nuclear factor κB adaptor protein, CARD14; and adaptor protein 1 complex, subunit 3 (AP1S3) have been discovered in European, Asian, and Pakistani populations. These may be inherited in a homozygous compound or simple heterozygous state. IL36RN mutations are most frequently associated with early-onset pustular psoriasis. Mutations in SERPINA1 and SERPINA3, and some MEFV variants, have also been associated with pustular psoriasis.

Pustular psoriasis may be preceded by or may coexist with plaque psoriasis. Pustular flares can be induced by infection (Trichophyton rubrum, cytomegalovirus, Streptococcus spp, varicella-zoster, and Epstein-Barr virus), a rapid withdrawal of corticosteroids, pregnancy, medications (NSAIDs, lithium, potassium iodine, trazodone, penicillin, interferon, and hydroxychloroquine), and topical irritants such as tar and anthralin. More recently, COVID-19 infection has been shown to trigger pustular flares of psoriasis.

While tumor necrosis factor (TNF)-alpha antagonists such as infliximab and adalimumab are used to treat pustular psoriasis, they have also been reported, paradoxically, to induce it.

Patients may experience relapses and remissions over a period of years. It may be precipitated by use and withdrawal from systemic corticosteroids.

Extracutaneous manifestations of pustular psoriasis may be severe and are associated with a great deal of morbidity and mortality. The most common extracutaneous manifestations of pustular psoriasis include cholestasis, cholangitis, arthritis, intestinal pneumonitis, oral lesions, and acute renal failure. Electrolyte disturbances such as hypocalcemia may occur and can be life-threatening. Lesions may also become superinfected.