Atopic Dermatitis Disease Background

Introduction

Atopic dermatitis is a familial, chronic, relapsing, inflammatory skin disease characterized by intense itching, and dry skin, with inflammation and exudation that commonly presents during early infancy and childhood; however, it can persist or start in adulthood. It is also referred to as atopic eczema, eczema, or neurodermatitis. 

Epidemiology

Atopic dermatitis affects as much as 230 million people worldwide. It is one of the most common skin diseases afflicting both children and adults with a prevalence of 2-10% in young adults and up to 20% in children while it is estimated to be present in 2-5% of adults. In the Asia-Pacific region, the prevalence of atopic dermatitis among 6- to 7-year-old children is approximately 10%, higher than the overall global prevalence which is at 7.9%. Likewise, the prevalence of the disease in the first 2 years of life is also high at 7-27% in Asian-Pacific countries. However, among 13- to 14-year-old adolescents, prevalence in Asian-Pacific countries were lower at 3-5% compared to the global average of 7%.

Additionally, the prevalence of atopic dermatitis has been steadily increasing in low- and middle-income countries. In Malaysia, the 12-month prevalence of the disease has risen from 9.5% (1994-1995) to 12.6% (2002-2003), with an increase of 0.49% yearly. Other countries like China, Korea, and India also showed increasing trends of atopic dermatitis. 

Etiology

Common causes of atopic dermatitis include allergens such as food, soaps, detergents, inhalant allergens, and skin infections. 

Pathophysiology

Heredity (80% in monozygous twins, 20% in heterozygous twins) influences atopic dermatitis. It is also known that some individuals with atopic dermatitis have increased IgE production. 

The presence of inherited loss-of-function defects in the filaggrin (FLG) gene increases the risk of developing atopic dermatitis. FLG is proteolyzed in the upper layers of the stratum corneum to produce the skin’s natural moisturizing factor (NMF). The lack of skin barrier and impairment of moisture retention capacity produce dry skin due to abnormalities in lipid metabolism and protein formation thus allowing entry of allergens, antigens, and chemicals from the environment. 

There is also susceptibility to infections caused by Staphylococcus aureus or epidermidis and Malassezia furfur through abnormal microbial colonization. The decreased diversity of the cutaneous microbiome secondary to Staphylococcus aureus colonization is significantly associated with atopic dermatitis flare-up.