What are the differences between atopic dermatitis (eczema) and psoriasis in terms of symptoms, treatment, and patient management?

Differentiating Atopic Dermatitis from Psoriasis

Atopic dermatitis presents with intensely pruritic, eczematous lesions showing weeping, crusting, and lichenification in flexural areas, while psoriasis manifests as well-demarcated, indurated plaques with silvery scale and less pruritus. 1, 2

Clinical Presentation Differences

Morphology and Appearance

• Atopic dermatitis shows erythematous papules with exudation and crusting in acute phases, progressing to chronic lichenified plaques with accentuated skin markings 1
• Psoriasis displays indurated plaques with characteristic silvery scale, deeply erythematous color, and well-demarcated borders without the oozing/crusting typical of eczema 2

Distribution Patterns

• Atopic dermatitis follows age-specific patterns: facial and extensor involvement in infants, predominantly flexural areas (antecubital and popliteal fossae) in older children and adults 1
• Psoriasis commonly affects extensor surfaces (elbows, knees), scalp, and trunk, with more symmetrical distribution 2

Pruritus Intensity

• Atopic dermatitis features intense pruritus as the dominant symptom, driving the itch-scratch cycle and often reported as scratching or rubbing in children 1, 3
• Psoriasis presents with significantly less pruritus, though over 85% of patients experience some degree of itch 3, 2

Key Diagnostic Distinguishing Features

Surface Characteristics

• Atopic dermatitis: Weeping, crusting, and generalized dry skin with eczematous changes 1
• Psoriasis: Silvery scale on indurated plaques without eczematous change 2

Erythrodermic Presentations

When both conditions present as erythroderma, differentiation becomes challenging but critical 2:

• Psoriasis: Areas of indurated plaques with silvery scale persist, deeply erythematous color, lack of "skip" areas 2
• Atopic dermatitis: More superficial exfoliation, oozing/crusting, less induration 2

Associated Features

• Atopic dermatitis: Personal or family history of atopic triad (asthma, allergic rhinitis, food allergies), elevated IgE levels 2, 4
• Psoriasis: Personal or family history of psoriasis, potential psoriatic arthritis with dactylitis ("sausage digits") 2

Complications and Superinfections

Bacterial Infections

• Atopic dermatitis: Staphylococcus aureus colonization is extremely common, presenting with golden-yellow crusts, increased weeping beyond typical presentation 1
• Psoriasis: Less prone to bacterial superinfection due to adequate antimicrobial peptide production 5

Viral Infections

• Atopic dermatitis: High risk for eczema herpeticum (herpes simplex infection) presenting as grouped, punched-out erosions and multiple discrete vesicles requiring immediate virological screening 1
• Psoriasis: Lower susceptibility to viral infections due to preserved antimicrobial defenses 5

Immunologic Differences

Cytokine Profiles

• Atopic dermatitis: Th2/Th22-polarized immune response with attenuated Th17 axis, leading to insufficient antimicrobial peptide induction and more severe barrier dysfunction 5, 6
• Psoriasis: Th17/IL-23 pathway activation predominates, with adequate antimicrobial peptide production 5, 6

Barrier Function

Both conditions share barrier dysfunction, but the mechanisms differ 5:

• Atopic dermatitis: Th2-dominant cytokine milieu actively down-regulates immunity against infections 5
• Psoriasis: Barrier dysfunction present but compensated by enhanced antimicrobial defenses 5

Treatment Approach Differences

First-Line Topical Therapy

• Atopic dermatitis: High-lipid content emollients applied liberally and frequently, medium-to-high potency topical corticosteroids 3-4 times daily for inflammation 4, 2
• Psoriasis: Mid-potency topical corticosteroids, vitamin D analogs, and emollients, often under occlusion 2

Phototherapy Considerations

Both conditions respond to phototherapy, but protocols may differ 2:

• Atopic dermatitis: Narrowband UVB is most commonly recommended due to low risk profile and efficacy 2
• Psoriasis: Multiple modalities effective including narrowband UVB, PUVA, and Goeckerman therapy 2

Systemic Therapy for Refractory Disease

• Atopic dermatitis: Cyclosporine, azathioprine, methotrexate, or mycophenolate mofetil when topicals and phototherapy fail 2
• Psoriasis: Biologic agents (TNF inhibitors, IL-12/23 inhibitors like ustekinumab, IL-17 inhibitors) are standard for moderate-to-severe disease 2, 6

Common Pitfalls to Avoid

Misdiagnosis in Erythrodermic Cases

The most difficult differential diagnosis occurs when either condition presents as erythroderma 2:

• Obtain detailed personal and family history of psoriasis or atopy 2
• Look for subtle clues: indurated plaques with silvery scale favor psoriasis; oozing and crusting favor atopic dermatitis 2
• Consider skin biopsy when diagnosis remains uncertain, though histology can overlap 2

Overlooking Superinfections in Atopic Dermatitis

Failure to recognize and treat bacterial or viral superinfections leads to treatment failure 1:

• Golden-yellow crusts and increased weeping indicate bacterial infection requiring bacteriological swabs 1
• Grouped erosions and vesicles suggest eczema herpeticum requiring immediate virological screening 1

Inappropriate Systemic Steroid Use

Systemic steroids should be avoided in atopic dermatitis except for acute severe exacerbations as short-term bridge therapy 2