Differentiating Psoriasis from Eczema
Psoriasis presents with well-demarcated erythematous plaques with silvery scale, minimal pruritus, and lacks oozing/crusting, while eczema shows poorly-defined eczematous lesions with intense pruritus, vesiculation, oozing, and crusting. 1
Key Clinical Distinguishing Features
Lesion Morphology
- Psoriasis: Well-demarcated, thick hyperkeratotic plaques with silvery-white scale; plaques are uniform and symmetric 1
- Eczema: Poorly-defined erythematous patches with vesicles, oozing, crusting, and excoriations; lesions are more variable in appearance 1
Pruritus Intensity
- Psoriasis: Minimal to moderate itching; pruritus is NOT a dominant feature 1
- Eczema: Severe, intense pruritus that drives scratching behavior and is the primary complaint 1
Surface Characteristics
- Psoriasis: Dry, thick scale without oozing or weeping; lacks eczematous changes 1
- Eczema: Vesicular eruptions, serous exudate, crusting, and weeping are characteristic findings 1
Distribution Patterns
- Hand involvement (when present): Psoriasis affects dorsal hands, wrists (both sides), nail folds, and nails; eczema involves palmar surfaces, palmar digits, and finger pulps 2
- Scalp involvement: Psoriasis shows thick, adherent scale with sharp borders; eczema shows diffuse scaling without clear demarcation 3, 4
Critical Diagnostic Pitfall
Recognize "eczematized psoriasis" (5-10% of psoriasis cases), which presents with severe itching, eosinophils on biopsy, serum crusts, and spongiosis—features typically seen in eczema. 5 This overlap condition may require molecular testing (NOS2 and CCL27 gene expression) for definitive diagnosis when clinical and histological features remain indistinct. 6
Management Algorithm
For Confirmed Psoriasis
- Initial therapy: Apply clobetasol propionate 0.05% or betamethasone dipropionate 0.05% twice daily for 2-4 weeks maximum 3, 4
- Combination approach: Add calcipotriol to topical corticosteroids for synergistic effect superior to monotherapy 3, 4
- Maintenance: Transition to weekend-only corticosteroid application with vitamin D analogs on weekdays after achieving control 4
- NEVER use systemic corticosteroids—they precipitate erythrodermic or generalized pustular psoriasis upon discontinuation 3, 7
For Confirmed Eczema (Atopic Dermatitis)
- Intensive clearance phase: Medium-to-high potency topical corticosteroids (class I-III US, III-IV Europe) once or twice daily for 1-4 weeks 1
- Proactive maintenance: Apply medium-strength corticosteroid or tacrolimus 2-3 times weekly to previously affected areas to prevent flares 1
- Patient education: Address trigger avoidance (irritants, detergents, sweat), adherence optimization, and topical steroid phobia before escalating therapy 1
- Infection screening: Identify and treat Staphylococcus aureus colonization and viral infections before considering systemic therapy 1
When Diagnosis Remains Uncertain
- Observe response to initial therapy: Psoriasis responds to high-potency corticosteroids with calcipotriol; eczema requires addressing triggers and may need wet wrap therapy 1, 3
- Consider skin biopsy: Histology showing eosinophils, spongiosis, and serum crusts favors eczema; uniform epidermal hyperplasia without these features favors psoriasis 1, 5
- Refer to dermatology when body surface area exceeds 5%, inadequate response after 8 weeks of optimized topical therapy, or diagnostic uncertainty persists 4
Location-Specific Modifications
Use low-potency corticosteroids (class 5-7) or topical calcineurin inhibitors on face, genitals, intertriginous areas, and forearms regardless of diagnosis to minimize atrophy risk. 4 High-potency agents on these sensitive areas cause irreversible skin damage including striae and telangiectasia. 4