Pustular psoriasis is an uncommon variant of psoriasis that is characterized by the presence of widespread, erythematous, sterile pustules on clinical examination and a predominantly neutrophilic infiltrate with intraepidermal and subcorneal pustules histopathologically. 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.

Pustular psoriasis may occur in men and women of all ages, as well as in children. Incidence peaks between the ages of 40 and 59 years. Pustular psoriasis has been estimated to account for about 1.5% of all psoriasis cases. Asian and Hispanic individuals are more commonly affected by pustular psoriasis compared to White individuals. Polyarthritis and metabolic syndrome are common associations. Some patients with a history of plaque psoriasis can develop pustular psoriasis, but the two conditions appear to have distinct genetic and pathophysiologic mechanisms.

The etiology of pustular psoriasis is incompletely understood, but cases have been associated with hypocalcemia, infection (Trichophyton rubrum, cytomegalovirus, Streptococcus spp, varicella-zoster virus, 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. While tumor necrosis factor (TNF)-alpha antagonists such as infliximab and adalimumab are used to treat pustular psoriasis, they have also been reported to paradoxically induce it.

Additionally, there is emerging evidence that pustular psoriasis is associated with mutations in the IL36RN gene that encodes the interleukin-36 receptor antagonist (IL-36RA). Mutations in this gene have been detected in different variants of pustular psoriasis, including generalized pustular psoriasis, impetigo herpetiformis, palmoplantar pustulosis, and the exanthematic type of pustular psoriasis. Deficiency of interleukin-36 (IL-36) receptor antagonist (DITRA) syndrome is an autoimmune inflammatory disorder caused by loss of function mutations in the IL36RN gene that manifests in early childhood with generalized pustular psoriasis, fever, leukocytosis, and elevated C-reactive protein (CRP) levels.

There are 4 subtypes of pustular psoriasis:

• von Zumbusch type (generalized pustular psoriasis) – 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; associated with fever, malaise, and other systemic manifestations.
• Localized pattern – Pustules appear in existing psoriatic plaques. This can be seen in active plaques. Palmoplantar pustular psoriasis is the most common form of localized pustular psoriasis. Acrodermatitis continua (AC), also known as Hallopeau disease and acrodermatitis continua of Hallopeau, is a form of localized pustular psoriasis in which involvement of the distal digits primarily is common.

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.

Nail involvement in pustular psoriasis is common and usually involves the nail matrix and nail bed. Pustules may be seen under the nail plate, and pain is common. The nail often becomes dystrophic; subsequent onycholysis and subungual hyperkeratosis may occur. Nail shedding is common, and when it occurs, lakes of pus and crusts are revealed on the denuded nail bed. In time, permanent scarring develops with partial or total loss of the nail plate. Occasionally, proximal spread of the disease or acroosteolysis of the distal phalanx occurs.

Extracutaneous manifestations of pustular psoriasis may be severe. 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.