Atopic dermatitis (AD) is a common, chronic inflammatory skin condition affecting up to 20% of children and 3% of adults worldwide. There is wide variation in the prevalence of AD among different countries. Although the frequency of AD is increasing in developing countries, it seems to have stabilized in developed countries, affecting approximately 1 in 5 schoolchildren. Adult-onset AD is not uncommon and is significantly higher, affecting between 11% and 13% of adults in some countries, for example, Singapore, Malaysia, and Sweden. AD is thus associated with significant health care economic burden in all age groups.
Key points
- •
Atopic dermatitis (AD) affects approximately 20% of schoolchildren in developed countries and approximately 3% of adults worldwide.
- •
Adult-onset AD is not uncommon, with a prevalence of 11% to 13% in some countries, for example, Singapore, Malaysia, and Sweden.
- •
Although the prevalence of AD is increasing in developing countries, the prevalence has stabilized in the developed countries.
- •
Erythema is not as pronounced on darker skin and may appear violaceous, which presents an obstacle to a physician making a diagnosis or assessing the severity of disease.
- •
Follicular or papular eczema and postinflammatory dyspigmentation are common in patients of color.
The severity and prevalence of AD may be increased in certain racial/ethnic populations, especially among blacks/African Americans. Erythema may be difficult to assess in patients with more darkly pigmented skin. Follicular or papular eczema and postinflammatory dyspigmentation are common in patients of color. Variations in the epidemiology of AD between different countries and ethnic groups may be due to differences in genetic predisposition, environmental, and socioeconomic factors.
Introduction
AD (or eczema) is a common inflammatory skin condition characterized by recurrent episodes of pruritus and a chronic, relapsing course. Having a persistent itch-scratch cycle, AD is associated with numerous complications, including secondary infections as well as significant comorbidities. There is an impactful global health care economic burden associated with AD, on which interesting ethnic/racial trends can be observed.
AD affects up to 20% of children and 3% of adults worldwide. Recent data show that the prevalence of AD is still increasing globally, especially in low-income countries. Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) demonstrated a significant difference in the prevalence and incidence of AD both within countries and between geographic areas. Scandinavia, Northern and Western Europe, Australasia, and urban areas in Africa suffered from the highest prevalence rates, whereas those in Eastern Europe, the Middle East, China, and Central Asia showed the lowest rates of prevalence. The reasons for such striking worldwide geographic variability in the epidemiology of AD are still unclear. Along with underlying genetic disposition, these variations have been attributed in part to environmental factors, including urbanization, climate, diet, aeroallergens, and infections.
Elucidating the racial disparity and epidemiology of AD will spur efforts to identify modifiable risk factors, which can contribute toward disease prevention. As such, the authors review advancements in AD epidemiology, including interracial and ethnic differences, reasons for such disparity, variability of clinical presentation, and disease severity.
Introduction
AD (or eczema) is a common inflammatory skin condition characterized by recurrent episodes of pruritus and a chronic, relapsing course. Having a persistent itch-scratch cycle, AD is associated with numerous complications, including secondary infections as well as significant comorbidities. There is an impactful global health care economic burden associated with AD, on which interesting ethnic/racial trends can be observed.
AD affects up to 20% of children and 3% of adults worldwide. Recent data show that the prevalence of AD is still increasing globally, especially in low-income countries. Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) demonstrated a significant difference in the prevalence and incidence of AD both within countries and between geographic areas. Scandinavia, Northern and Western Europe, Australasia, and urban areas in Africa suffered from the highest prevalence rates, whereas those in Eastern Europe, the Middle East, China, and Central Asia showed the lowest rates of prevalence. The reasons for such striking worldwide geographic variability in the epidemiology of AD are still unclear. Along with underlying genetic disposition, these variations have been attributed in part to environmental factors, including urbanization, climate, diet, aeroallergens, and infections.
Elucidating the racial disparity and epidemiology of AD will spur efforts to identify modifiable risk factors, which can contribute toward disease prevention. As such, the authors review advancements in AD epidemiology, including interracial and ethnic differences, reasons for such disparity, variability of clinical presentation, and disease severity.
Diagnosis and definition
Epidemiologic studies essentially rely on accurate definitions of a disease. AD demonstrates significant clinical variability and has proved a challenge for the establishment of accurate diagnostic criteria. The first set of standardized diagnostic criteria was developed by Hanifin and Rajka in 1980, in which affected patients must possess at least 3 major and 3 minor criteria to satisfy a diagnosis of AD ( Box 1 ). The United Kingdom Working Party revision of 1990 furthered the development of a standardized criteria, which revealed a sensitivity of 87.9% and a specificity of 92.8% when evaluated in a hospital outpatient setting ( Box 2 ). This was generally limited, however, to those with mild to moderate forms of typical AD. In clinical practice, diagnosis is often established based on a pruritic relapsing condition in typical locations, including the neck, face, and extensor surfaces in children and infants.
Major criteria (must have at least 3)
Pruritus
Typical morphology and distribution
Adults: flexural lichenification or linearity
Children and infants: involvement of facial and extensor
Surfaces
Chronic or relapsing dermatitis
Personal or family history of atopy
Minor criteria (must have at least 3)
Xerosis
Ichthyosis/keratosis pilaris/palmer hyperlinearity
Immediate (type 1) skin test reactivity
Elevated serum IgE
Early age at onset
Tendency to skin infections ( Staphylococcus aureus , herpes simplex)/impaired cellular immunity
Hand/foot dermatitis
Nipple eczema
Conjunctivitis
Dennie-Morgan fold
Keratoconus
Anterior subcapsular cataracts
Orbital darkening
Facial pallor/erythema
Pityriasis alba
Anterior neck folds
Itch when sweating
Intolerance to wool and lipid solvents
Perifollicular accentuation
Food intolerance
Course influenced by environmental/emotional factors
White demographic/delayed blanch
All patients must have an itchy skin condition in the last 12 months and have 3 or more of the following:
- •
History of involvement of the skin creases, such as antecubital, popliteal, dorsal ankles, or neck
- •
A personal history of asthma or hay fever (or history in first-degree relative in those under the age of 4)
- •
A history of generally dry skin during the last year
- •
Visible flexural dermatitis (or dermatitis of checks or forehead and outer limbs in children less than the age of 4
- •
Onset under the age of 2 (not used if child is under the age of 4)
Racial disparity
The ISAAC, an international multicountry cross-sectional survey of school children, was conducted to investigate the epidemiology, geographic variability, and trends in the prevalence of asthma, rhinitis, and AD. The ISAAC Phase One study was conducted in the early to mid-1990s. The ISAAC Phase Three was carried out approximately 7 years later using the same methodology and survey questionnaire to monitor the evolution in the prevalence of these disorders. This follow-up study involved 193,404 children ages 6 years to 7 years from 66 centers in 37 countries and 304,679 children ages 13 years to 14 years from 106 centers in 56 countries. Odhiambo and colleagues analyzed data from the study and found a wide variation in prevalence values worldwide, from 0.9% in India to 22.5% in Ecuador at ages 6 years to 7 years and from 0.2% in China to 24.6% in Colombia at ages 13 years to 14 years. This study, along with other smaller population-based and community-based studies, suggests an overall higher AD prevalence in wealthier, developed nations compared with poorer, developing nations.
Ethnic variation in the East
In the Asia-Pacific region, the 12-month prevalence of AD in children ages 13 years to 14 years was reported to be as high as 9% in Malaysia and Singapore and as low as 0.9% in China. China demonstrated the lowest AD prevalence in the world. The reasons for these differences in AD prevalence are poorly understood, but industrialization and socioeconomic factors have been implicated. Significantly, ISAAC Phase Three also highlighted the Asia-Pacific as an area of increasing AD prevalence. Of the 44 centers with an increase in prevalence, 10 were from the Asia-Pacific, hence putting this region second to Western Europe for centers with an increase in AD prevalence.
In Singapore, data derived from the ISAAC surveys indicated a modest increase in prevalence of AD among the age groups studied but an increased severity of symptoms in the 12-year to 15-year age group. This is further supported by a cross-sectional epidemiologic study by Tay and colleagues involving 12,323 students in Singapore (7-year, 12-year, and 16-year age groups), reporting a prevalence of AD of 20.8%, a frequency markedly higher than that reported in younger age groups. A recent community-based study of 681 randomly selected residents dwelling in public housing in Singapore showed a prevalence of AD of 20.6% in children (MJA Koh, personal communication, 2016) suggesting that the prevalence of AD in developed countries like Singapore has stabilized and is no longer increasing.
Age disparity
The diagnosis of AD is established by 1 year in 60% to 65% and by 5 years of age in 85% to 90% of children who have the disease. Subsequently, up to a third of children have eczema that persists into adulthood. Infantile AD is characterized by erythematous, oozing, excoriated plaques on the cheeks (sparing the nose), scalp, trunk, and extensor surfaces. In contrast, adult AD often presents as eczema of the hands and feet.
The prevalence of adult AD in the Western population was assessed to range from 1% to 3%. In contrast, the prevalence of adult AD among Asian populations seems higher.
Saeki and colleagues evaluated the prevalence of AD in Japanese adults at Kinki University and Asahikawa Medical College. A total of 2137 adult patients were examined. The prevalence of AD was 6.1% overall, and 10.5%, 7.8%, 3.9%, and 2.5%, respectively, for those in their 20s, 30s, 40s, and 50s/60s.
Sugiura and colleagues compared the disease prevalence of AD in Japan and found that in 1967, 73.9% of patients with AD were children ages 0 to 9 years at the Branch Hospital of the University of Tokyo, but this figure gradually dropped to 23.4% by 1996. On the contrary, the percentage of adult patients ages 20 to 29 years with AD was 3.1% in 1967 and markedly increased to 38.7% by 1996.
In the same vein, the pattern of AD in Singapore demonstrates a significant proportion of adult-onset AD, with 13.6% of the study cohort having a later onset of symptoms above 21 years of age. Findings were similar to another study carried out in Malaysia, where 13% of the patients had onset of AD after the age of 21 years. The recent community-based study of public housing residents in Singapore showed similar trends: a prevalence of AD of 11.1% in adults.
In contrast, a lower prevalence of AD among Korean adults was reported by Kim and colleagues : 2.6% overall, and 2.4%, 4.5%, 3.2%, 1.2%, and 0.4%, respectively, for those in their 10s/20s, 30s, 40s, 50s, and 60s and older.
In analyzing the data presented by Ronmark and colleagues involving 18,087 adults from Sweden, an incidence of AD of 11.5% (16–75 years) was found, which suggests that adult AD may not be uncommon worldwide.
Differences in phenotype
AD essentially presents the same across different racial and ethnics groups. There exist several key differentiating factors, however, which are more typical among patients of darker skin types, that must be considered.
First, erythema is less obvious in skin of color and may often appear violaceous. This can present a challenge to physicians making a diagnosis and assessing the severity of AD. Erythema is a feature that is included in several scoring tools, including Scoring Atopic Dermatitis and Eczema Area and Severity Index. This may lead to a delay in diagnosis and treatment and a more severe disease progression.
Second, patients with skin of color may manifest with follicular, papular, or lichenoid eczema as their primary disease phenotype ( Fig. 1 ). Facial and eyelid dermatitis are more common in female Asians, infants, and teenagers.
