Atopic Dermatitis: Medical Definition and Characteristics
Atopic dermatitis is a chronic, pruritic inflammatory skin disease characterized by intense itching, eczematous lesions, a relapsing course, and association with elevated IgE levels and personal or family history of atopy. 1
Definition and Pathophysiology
Atopic dermatitis (AD), also known as atopic eczema, is a chronic inflammatory skin condition with complex pathophysiology involving:
- Dual mechanisms: Both immunologic aberration triggering barrier disruption ("inside-out") and skin barrier dysfunction ("outside-in") 1
- Genetic predisposition: Strong genetic component affecting skin barrier function
- Immune dysregulation: Primarily T-cell driven inflammation with dominant type-2 mechanisms 2
- Epidermal barrier dysfunction: Leading to increased transepidermal water loss and penetration of allergens and irritants
Clinical Presentation
Cardinal Features
- Intense pruritus: The hallmark symptom essential for diagnosis 3
- Eczematous lesions: Erythema, edema, xerosis, erosions/excoriations, oozing, crusting, and lichenification 1
- Chronic relapsing course: Characterized by exacerbations and remissions
- Atopic associations: Personal or family history of asthma, allergic rhinitis, or food allergies 1
Age-Specific Distribution
- Infants: Face, scalp, and extensor surfaces
- Children: Flexural areas (antecubital and popliteal fossae)
- Adults: Flexural areas, face, neck, and upper torso 1
Diagnostic Criteria
AD diagnosis is made clinically based on:
- Historical features
- Morphology and distribution of skin lesions
- Associated clinical signs 1
Epidemiology
- Prevalence: Affects 11-20% of children and 5-10% of adults in developed countries 4
- Onset: 60% develop symptoms in the first year of life and 90% by 5 years of age 1
- Persistence: 10-30% of childhood cases persist into adulthood 1
- Increasing trend: Rising prevalence over past decades in many countries 1, 2
Comorbidities and Complications
Atopic Conditions
- Asthma: Adults with AD are 3 times more likely to have asthma compared to the general population 1
- Allergic rhinitis/rhinoconjunctivitis: Commonly associated with AD 1
- Food allergies: Particularly relevant in early life 1
Other Comorbidities
- Sleep disturbance: Affects up to 60% of children with AD, increasing to 83% during exacerbations 1
- Mental health disorders: Depression noted in both teens and adults with AD 1
- Behavioral disorders: Possible association with ADHD in children, though causality is not established 1
Complications
- Skin infections: Increased risk of bacterial (primarily Staphylococcus aureus), viral (eczema herpeticum), and fungal infections 3
- Quality of life impairment: Significant impact due to chronic pruritus, sleep disturbance, and visible skin lesions 1
Clinical Impact
Morbidity: Significant impact on quality of life due to:
- Persistent pruritus leading to sleep disturbance
- Visible skin lesions affecting self-esteem
- Chronic nature requiring ongoing management
Disease burden: AD represents a considerable health and socioeconomic burden 4
Differential Diagnosis
When evaluating potential AD, consider:
- Seborrheic dermatitis (yellowish, greasy scales in sebaceous gland-rich areas) 3
- Contact dermatitis
- Psoriasis
- Scabies
- Fungal infections (typically with annular lesions and well-defined borders) 3
- Primary immunodeficiencies with eczematous features 1
Key Distinguishing Features
- Location: AD typically affects flexural areas but spares axillary and inguinal folds 3
- Pruritus: Intense itching is essential for AD diagnosis, unlike seborrheic dermatitis which has mild or no pruritus 3
- Skin appearance: AD presents with poorly defined borders and generalized xerosis, while seborrheic dermatitis has well-defined borders and greasy appearance 3
Understanding these distinctive medical characteristics of atopic dermatitis is essential for accurate diagnosis and effective management of this chronic inflammatory skin condition.