It is unclear whether impetigo herpetiformis is a separate entity from generalized pustular psoriasis (GPP). Many women who develop impetigo herpetiformis have no personal or family history of psoriasis and are never symptomatic outside of pregnancy. However, some women with biopsy-proven pustular psoriasis in pregnancy subsequently develop GPP later in life.
Pathogenesis is poorly understood given the limited number of cases, but it may be related to the increase in progesterone in late pregnancy. Impetigo herpetiformis can also arise during menstrual cycles and affect patients taking oral contraceptive pills, further supporting a role of hormones in pathogenesis. Some authors relate impetigo herpetiformis to hypocalcemia in late pregnancy due to volume expansion and increased renal clearance.
The eruption usually begins in the third trimester of pregnancy (after 26 weeks) but may occur at any time during pregnancy. It begins as erythematous plaques with circumferential rings of pustules. Plaques can become centrally eroded as they enlarge, and patients may experience an itching or burning sensation, especially at the margins. Plaques often arise first in intertriginous areas and expand to the trunk and extremities symmetrically. The head, hands, and feet are usually spared. Pustular psoriasis of pregnancy may affect oral and esophageal mucous membranes, and subungual pustules can result in onycholysis.
The rash may be accompanied by systemic symptoms including fever, chills, nausea, vomiting, lymphadenopathy, seizure, and malaise. It commonly recurs in subsequent pregnancies, typically with earlier onset and greater severity with each successive pregnancy. Maternal complications include electrolyte imbalance, fluid loss, and sepsis from secondary infection. Hypocalcemia can result in delirium, tetany, and convulsions. Fetal complications include placental insufficiency, intrauterine fetal demise, neonatal death, and low birth weight.
L40.1 – Generalized pustular psoriasis
65539006 – Impetigo Herpetiformis
Differential Diagnosis & Pitfalls
- Impetigo – Exclude with culture.
- Candidiasis – Exclude with culture.
- Acute generalized exanthematous pustulosis
- IgA pemphigus
- Subcorneal pustular dermatosis
- Polymorphic eruption of pregnancy (PEP), also called pruritic urticarial papules and plaques of pregnancy (PUPPP) – Intensely pruritic papules often found on or adjacent to striae on the abdomen and extremities. Papules fade into erythematous plaques. The disease is benign and self-limited and resolves after delivery.
- Atopic eruption of pregnancy – Patients may present with prurigo of pregnancy (atopic eruption of papules and nodules on extensor surfaces), pruritic folliculitis of pregnancy (follicular distribution of lesions, typically on trunk), or eczema in pregnancy (widespread pruritic eczematous papules and plaques favoring the flexural surfaces).
- Pemphigoid gestationis (herpes gestationis) – Subepidermal blisters seen in the bullous stage. Immunofluorescence shows bright linear C3 deposition in basement membrane.
- Intrahepatic cholestasis of pregnancy – Can cause pruritic rash. Check total serum bile acids to rule out.
- Dermatitis herpetiformis – Associated with celiac disease and has characteristic histology and granular IgA on immunofluorescence.