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Atopic dermatitis is the most common type of eczema, an inflammatory condition that causes disruption of the skin barrier. The onset of symptoms is often during childhood and is seen equally in both sexes. It affects around 1/20 children and 1/10 adults and is one of the leading chronic diseases worldwide, contributing significantly to economic burden and reduced quality of life. Atopic dermatitis is present in all races, however, a few epidemiological studies have shown evidence of increased prevalence in those of African and Asian descent. There has been a significant increase in the overall prevalence, especially in industrialized nations.
What causes Atopic Dermatitis?
The etiology of atopic dermatitis is thought to be multifactorial, involving the exposure to an environmental insult that causes an abnormal immune reaction in those with a predisposition for immune dysfunction and abnormalities in filaggrin protein. There is also some evidence of the influence of the microbiota of the skin and intestines on the risk of development of atopic dermatitis.
The stratum corneum acts as a barrier against external allergens, irritants, and infective agents while preserving adequate hydration through components such as natural moisturizing factors. Filaggrin proteins within this layer are vital in this process, as they bind the structural proteins of the epidermal cells, locking them and the other components in. Abnormalities in the filaggrin gene can predispose the skin barrier to damage when exposed to irritants or trauma, allowing the loss of lipids and moisturizing factors that results in trans-epidermal water loss and deeper penetration by the allergens.
An immune dysregulation that is characterized by abnormalities in the T-helper cells, most often Th2 cells, is also implicated in the pathogenesis. The T-helper cells are activated by epidermal inflammatory dendritic and innate lymphoid cells in response to disruption of the skin barrier, and release cytokines into the skin, including IL-13, which cause severe pruritus around the lesion. Scratching the affected area leads to further trauma and hypersensitization of the histamine-sensitive C-nerve fibers and consequently more inflammation.
The environmental factors leading to flares in atopic dermatitis can include cleaning products, cosmetics, certain foods, synthetic fabrics, pollution, heat, UV radiation, and hard water.
Signs and symptoms of Atopic Dermatitis
Severe pruritus characterized by an itch-scratch cycle is the most common symptom of atopic dermatitis. Diagnosis of atopic dermatitis is determined by pruritus, a chronic or relapsing history of the disease, xerosis, and a history of eczema. The clinical features of the eczematic lesions may depend on the age of the patient.
Other supporting symptoms and associated features include:
- Personal or family history of other atopic conditions, such as asthma and hay fever.
- Onset of disease in early childhood.
- Immunoglobulin E reactivity.
- Abnormal vascular response, such as pallor and white dermographism.
- Hertoghe’s sign (loss of lateral third of eyebrow).
- Perioral changes.
- Keratosis pilaris.
- Prurigo nodularis.
Ständer, S. (2021). Atopic Dermatitis. New England Journal of Medicine, 384(12), 1136–1143. https://doi.org/10.1056/nejmra2023911