Eczema herpeticum is a potentially life-threatening viral infection caused by widespread cutaneous dissemination of herpes simplex virus, most commonly type 1, occurring predominantly in patients with atopic dermatitis whose compromised skin barrier and dysregulated cutaneous immune responses render them uniquely vulnerable to the uncontrolled spread of herpetic infection beyond the localized cold sore or genital lesion that characterizes herpes simplex infection in immunologically normal individuals. The condition, first described by the Hungarian dermatologist Moriz Kaposi in 1887 under the designation Kaposi varicelliform eruption, produces a dramatic and alarming clinical picture of numerous painful, punched-out, umbilicated vesicles and erosions erupting in clusters across the atopic skin, with fever, malaise, and systemic illness reflecting the viremic dissemination of the virus from the primary cutaneous site of replication to distant organs. Without prompt recognition and initiation of systemic antiviral therapy, eczema herpeticum can progress to herpetic viremia with involvement of the central nervous system, eyes, liver, lungs, and adrenal glands, producing potentially fatal systemic herpetic disease.
The epidemiology of eczema herpeticum reflects the intersection of two highly prevalent conditions: atopic dermatitis, affecting fifteen to thirty percent of children and two to ten percent of adults in developed countries, and herpes simplex virus type 1 infection, which infects approximately sixty to seventy percent of the global adult population as a primary infection typically acquired in childhood or young adulthood. Despite this high background prevalence of both atopic dermatitis and herpes simplex virus carriage, eczema herpeticum is a relatively uncommon complication of atopic dermatitis, estimated to occur in approximately three percent of atopic dermatitis patients, suggesting that additional host factors beyond atopic dermatitis diagnosis and herpes simplex virus exposure are required for the development of this severe complication. These additional vulnerability factors include greater atopic dermatitis severity, particularly the combination of widespread skin barrier disruption with depressed innate antiviral immunity that characterizes severe atopic disease, younger age at first herpes simplex virus exposure before robust antiviral immunity has developed, and possibly genetic variants in innate immune pathways that reduce the cutaneous antiviral response.
The clinical significance of eczema herpeticum extends beyond its acute morbidity to include the long-term implications of primary herpes simplex virus infection in patients with atopic dermatitis, who face a higher risk of recurrent eczema herpeticum episodes with subsequent herpes simplex virus reactivations than the general population faces with recurrent herpes labialis. Each recurrent episode carries the same risks of dissemination and severe complications as the primary episode, though recurrences are typically less severe in patients who have developed partial antiviral immunity through prior exposure. The management of recurrent eczema herpeticum, including the role of long-term suppressive antiviral therapy in preventing recurrences in patients with frequent episodes, represents an important clinical consideration in the long-term management of patients with atopic dermatitis and a history of this complication.
Immunological Vulnerability in Atopic Dermatitis
The specific vulnerability of atopic dermatitis patients to eczema herpeticum reflects multiple immunological abnormalities that collectively impair the cutaneous antiviral defense mechanisms that normally prevent herpes simplex virus from disseminating beyond the initial site of infection. In normal skin, the innate immune response to herpes simplex virus infection is rapidly activated through the recognition of viral DNA and dsRNA replication intermediates by pattern recognition receptors including toll-like receptor 9 and the cytosolic cGAS-STING pathway, triggering the production of type I interferons that restrict viral replication in surrounding keratinocytes and activate natural killer cells that eliminate virus-infected cells before adaptive immune responses are established.
In atopic dermatitis skin, this innate antiviral interferon response is profoundly impaired through mechanisms directly attributable to the Th2-polarized cytokine environment that drives the atopic inflammatory response. Interleukin-4 and interleukin-13, the signature Th2 cytokines whose overproduction defines atopic dermatitis, suppress the production of interferon alpha, interferon beta, and interferon lambda by keratinocytes and plasmacytoid dendritic cells in response to viral stimuli, creating a local immunological environment in which herpes simplex virus replication encounters significantly reduced interferon-mediated resistance. The reduced expression of antimicrobial peptides including human beta defensins 2 and 3 and the cathelicidin LL-37 in atopic dermatitis skin, also attributable to Th2 cytokine-mediated suppression, removes an additional layer of innate antiviral defense, since LL-37 in particular has direct virucidal activity against herpes simplex virus at concentrations achievable in normal skin.
The skin barrier disruption of atopic dermatitis provides the physical gateway through which herpes simplex virus, transmitted from the cold sore or genital lesion of an infected contact, enters the skin at sites of barrier compromise. Once through the disrupted stratum corneum, the virus encounters the keratinocyte layers of the epidermis in an immunologically permissive environment created by the interferon deficiency and antimicrobial peptide deficiency described above, enabling uncontrolled viral replication and lateral spread through the epidermis that produces the characteristic widespread distribution of eczema herpeticum lesions. The predilection of eczema herpeticum lesions for previously or currently eczematous skin reflects both the portal of entry provided by the disrupted barrier and the local immunological vulnerability of inflamed atopic skin to herpetic spread.
Clinical Presentation and Diagnosis
The clinical diagnosis of eczema herpeticum is based on the recognition of its characteristic lesion morphology in the clinical context of atopic dermatitis with a history of herpes simplex virus exposure or infection. The primary lesion of eczema herpeticum is a small vesicle or pustule, typically two to three millimeters in diameter, with a central umbilication or depression that distinguishes herpetic vesicles from the eczematous vesicles of the underlying atopic dermatitis and from the vesicles of other viral eruptions. These umbilicated vesicles occur in clusters and progress through a rapid sequence of crusting, erosion, and punched-out ulceration as the virus-infected keratinocytes undergo cytopathic destruction, producing the painful, crusted erosions with a distinctive punched-out appearance that are the most clinically recognizable lesions of established eczema herpeticum.
The distribution of eczema herpeticum lesions reflects the pattern of skin barrier disruption in the individual patient, with the head and neck being the most commonly affected regions because atopic dermatitis frequently involves these sites and because oral herpes simplex virus type 1 from perioral cold sores or herpetic gingivostomatitis provides the inoculum for cutaneous infection. However, the lesions can involve any body surface with atopic skin changes, including the trunk and extremities, and in severe cases can coalesce to involve a large proportion of the body surface area in a distribution that may resemble erythroderma. Periocular involvement, in which eczema herpeticum lesions affect the eyelid skin and potentially the ocular surface, requires urgent ophthalmological evaluation because herpetic keratitis and anterior uveitis can produce permanent visual impairment if not promptly treated with topical antiviral therapy.
The systemic symptoms of eczema herpeticum, including high fever often exceeding 39 degrees Celsius, profound malaise, tender lymphadenopathy draining the affected skin areas, and in severe cases the features of herpetic viremia including hepatitis, encephalitis, pneumonitis, and adrenal insufficiency, reflect the systemic dissemination of the virus and the intensity of the host inflammatory response to widespread viral infection. Laboratory findings may include leukocytosis or leukopenia, elevated liver transaminases indicating hepatic involvement, and elevated inflammatory markers. The presence of herpetic viremia can be confirmed by herpes simplex virus polymerase chain reaction testing of peripheral blood, which also provides viral load quantification that correlates with disease severity and can be used to monitor treatment response.
The laboratory confirmation of eczema herpeticum is important for directing antiviral therapy and for distinguishing eczema herpeticum from the other infectious and non-infectious conditions that may produce similar clinical appearances. Viral swab from the base of an unroofed fresh vesicle or a moist erosion, submitted for herpes simplex virus polymerase chain reaction testing, provides the most sensitive and specific diagnostic method and can produce a result within hours in facilities with on-site molecular diagnostics. The Tzanck smear, in which material from a vesicle base is stained and examined for the multinucleated giant cells and intranuclear inclusion bodies characteristic of herpetic infection, provides a rapid bedside test whose sensitivity is substantially lower than polymerase chain reaction but whose immediacy may guide initial antiviral therapy decisions pending confirmatory molecular results.
Antiviral Treatment and Supportive Care
The treatment of eczema herpeticum requires prompt initiation of systemic antiviral therapy targeting herpes simplex virus replication, with intravenous aciclovir being the standard of care for moderate to severe presentations requiring hospitalization and oral aciclovir or valaciclovir being appropriate for mild cases managed in the outpatient setting in clinically stable, reliable patients. The decision between intravenous and oral antiviral therapy is guided by the severity of the cutaneous eruption, the presence or absence of systemic features suggesting herpetic viremia, the patient’s ability to absorb oral medications reliably given the gastrointestinal symptoms that may accompany severe eczema herpeticum, and the degree of immunosuppression from concurrent atopic dermatitis treatments that may impair viral clearance.
Intravenous aciclovir, administered at doses of five to ten milligrams per kilogram every eight hours in adults with adequate renal function, achieves plasma concentrations substantially higher than those achievable with oral administration and ensures reliable drug delivery independent of gastrointestinal absorption, making it the preferred route for severe eczema herpeticum with systemic features, extensive cutaneous involvement, periocular disease, or evidence of visceral dissemination. The duration of intravenous aciclovir treatment is typically continued until clinical improvement is established, generally five to ten days, after which transition to oral valaciclovir can complete the antiviral course. Renal function monitoring during intravenous aciclovir therapy is essential because aciclovir crystalluria can precipitate acute kidney injury particularly at higher doses or in patients with pre-existing renal impairment or hypovolemia.
The management of the underlying atopic dermatitis during eczema herpeticum requires careful consideration of the immunological balance between suppressing the atopic inflammation that promotes viral spread and maintaining sufficient antiviral immune competence to clear the herpetic infection. Topical corticosteroids and calcineurin inhibitors are generally withheld from affected areas during active eczema herpeticum because of their local immunosuppressive effects that could impair antiviral responses, though they may be continued on unaffected atopic skin to prevent further skin barrier compromise that could expand the area of viral vulnerability. The use of dupilumab during active eczema herpeticum is controversial given its theoretical potential to suppress Th1 antiviral immune responses alongside Th2 atopic inflammation, and clinical judgment regarding its continuation or temporary interruption should be guided by the severity of the herpetic infection and the atopic disease. Following resolution of eczema herpeticum, optimization of atopic dermatitis management to reduce skin barrier disruption and cutaneous inflammation represents the most important long-term strategy for reducing the risk of recurrent herpetic episodes.