Eczema herpeticatum

Disseminated life-threatening viral skin rash in a child with atopic dermatitis

We report the case of a toddler, with a history of mild atopic dermatitis (AD) since early infancy, presented to the Giannina Gaslini, a pediatric polyclinic hospital, 14 days after measles-mumps-rubella (MMR) vaccination, for the occurrence of a disseminated vesico-pustular rash, accompanied by general malaise, fever, restlessness, and anorexia. Eczema herpeticum (EH) was diagnosed clinically and confirmed by laboratory examinations. The exact pathogenesis of EH in AD is still debated and possibly involves an inter-play between altered cell-mediated and humoral immunity, failure to up-regulate antiviral proteins, and exposure of viral binding sites through the dermatitis and an epidermal barrier failure. We hypothesize that in this particular case, MMR vaccination might have played an additional important role in the alteration of innate immune response, facilitating the manifestation of herpes simplex virus type 1 in the form of EH.

Narrative review on the management of moderate-severe atopic dermatitis in pediatric age of the Italian Society of Pediatric Allergology and Immunology (SIAIP), of the Italian Society of Pediatric Dermatology (SIDerP) and of the Italian Society of Pediatrics (SIP)

Currently, there are a few detailed guidelines on the overall management of children and adolescents with moderate-severe atopic dermatitis. AD ​​is a complex disease presenting with different clinical phenotypes, which require an individualized and multidisciplinary approach. Therefore, appropriate interaction between primary care pediatricians, pediatric allergists, and pediatric dermatologists is crucial to finding the best management strategy. In this manuscript, members of the Italian Society of Pediatric Allergology and Immunology (SIAIP), the Italian Society of Pediatric Dermatology (SIDerP), and the Italian Society of Pediatrics (SIP) with expertise in the management of moderate-severe atopic dermatitis have reviewed the latest scientific evidence in the field. This narrative review aims to define a pathway to appropriately managing children and adolescents with moderate-severe atopic dermatitis.

Eczema herpeticum in atopic dermatitis

Atopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases leading to pruritic skin lesions. A subset of AD patients exhibits a disseminated severe HSV infection called eczema herpeticum (EH) that can cause life-threatening complications. This review gives an overview of the clinical picture, and characteristics of the patients as well as the diagnosis and therapy of EH. A special focus lies on the pathophysiological hallmarks identified so far that predispose for EH. This aspect covers genetic aberrations, immunological changes, and environmental influences displaying a complex multifactorial situation, which is not completely understood. Type 2 skewing of virus-specific T cells in ADEH⁺ patients has been implicated in immune profile abnormalities, along with impaired functions of dendritic cells and natural killer cells. Furthermore, aberrations in interferon pathway-related genes such as IFNG and IFNGR1 have been identified to increase the risk of EH. IL-4, IL-25, and thymic stromal lymphopoietin (TSLP) are overexpressed in EH, whereas antimicrobial peptides like human β-defensins and LL-37 are reduced. Concerning the epidermal barrier, single nucleotide polymorphisms (SNPs) in skin barrier proteins such as filaggrin were identified in ADEH⁺ patients. A dysbalance of the skin microbiome also contributes to EH due to an increase of Staphylococcus aureus, which provides a supporting role to the viral infection via secreted toxins such as α-toxin. The risk of EH is reduced in AD patients treated with dupilumab. Further research is needed to identify and specifically target risk factors for EH in AD patients.

Innate immunity in atopic dermatitis

Atopic dermatitis (AD) is a clinically defined, highly pruritic, chronic inflammatory skin disease. In AD patients, the combination of a genetic predisposition for skin barrier dysfunction and dysfunctional innate and adaptive immune responses leads to a higher frequency of bacterial and viral skin infections. The innate immune system quickly mobilizes an unspecific, standardized first-line defense against different pathogens. Defects in this system lead to barrier dysfunction which results in increased protein allergen penetration through the epidermis and predisposes to secondary skin infections. Two loss-of-function mutations in the epidermal filaggrin gene are associated with AD. Also, inducible endogenous antibiotics such as the antimicrobial peptides cathelicidin and the beta-defensins may show defective function in lesional AD skin. Eczema herpeticum is a disseminated viral infection almost exclusively diagnosed in AD patients, which is based on unmasking of the viral entry receptor nectin-1, lack of cathelicidin production by keratinocytes, and depletion of Type I IFN-producing plasmacytoid dendritic cells from AD skin. Future therapeutic approaches to AD may include enhancement of impaired innate in addition to downregulation of dysfunctional adaptive immunity.