Eczema vs Psoriasis and seborrheic dermatitis
How to tell Eczema and Psoriasis and seborrheic dermatitis apart when a board question makes them look alike.
Eczema is itchy flexural atopy; psoriasis is extensor silvery plaques; seborrheic dermatitis is greasy scale in sebum-rich areas.
Side by side
Eczema causes pruritic eczematous dermatitis with flexural involvement, xerosis, atopy, and spongiotic dermatitis.
Psoriasis causes well-demarcated plaques with silvery scale on extensor surfaces; seborrheic dermatitis causes greasy scale on scalp, face, and intertriginous areas.
Atopic dermatitis reflects barrier dysfunction, Th2 inflammation, and itch-scratch cycle.
Psoriasis is immune-mediated keratinocyte hyperproliferation; seborrheic dermatitis is inflammatory response in sebum-rich Malassezia-colonized areas.
Flexural itchy lichenified plaques and atopic history support eczema.
Auspitz sign and extensor plaques support psoriasis; greasy scalp/nasolabial scale supports seborrheic dermatitis.
The trap
All three are chronic scaly rashes, but distribution, scale quality, itch, and atopic history decide. ECZEMA (atopic dermatitis) is intensely PRURITIC, occurs on FLEXURAL surfaces (antecubital and popliteal fossae, neck), with poorly defined erythematous patches, vesicles, weeping, lichenification with chronicity; classic in patients with the atopic triad (asthma, allergic rhinitis, eczema); treat with emollients, topical steroids, topical calcineurin inhibitors (tacrolimus, pimecrolimus), dupilumab for severe. PSORIASIS is well-demarcated salmon-colored plaques with thick SILVERY SCALE on EXTENSOR surfaces (elbows, knees, scalp, sacrum); Auspitz sign (bleeding points on scale removal), Koebner phenomenon (lesions at sites of trauma), nail pitting and oil-drop sign; histology shows parakeratosis and Munro microabscesses; associated with psoriatic arthritis (dactylitis, distal interphalangeal involvement, pencil-in-cup deformity); treat with topical steroids and vitamin D analogs for mild disease; phototherapy or biologics (TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors) for severe. SEBORRHEIC DERMATITIS is greasy YELLOW scale in sebum-rich areas (scalp = dandruff, eyebrows, nasolabial folds, retroauricular, central chest), associated with Malassezia yeast overgrowth; classic in infants (cradle cap) and adults with Parkinson disease, HIV, or stress; treat with antifungal shampoos (ketoconazole) and low-potency steroids.
Watch it explained
The repair move
For scaly dermatitis, map distribution and scale quality before naming the rash.
Try a free question
CoreA 4-year-old boy with a history of asthma and allergic rhinitis has chronic itchy, erythematous, lichenified patches in the antecubital and popliteal fossae. His mother has the same. Skin biopsy shows spongiotic dermatitis. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Atopic dermatitis (eczema). Atopic dermatitis (eczema) is a chronic relapsing pruritic dermatitis in flexural distribution, associated with the atopic triad (asthma, allergic rhinitis, eczema), with spongiotic histology; treatment is emollients, topical corticosteroids, and topical calcineurin inhibitors.
Why the other choices are tempting
- B. Psoriasis features well-demarcated silvery scaly plaques on EXTENSOR surfaces with parakeratosis and Munro microabscesses on histology.
- C. Seborrheic dermatitis has greasy yellow scale on sebum-rich areas (scalp, eyebrows, nasolabial folds).
- D. Contact dermatitis follows specific antigen exposure with linear or geometric pattern.
- E. Lichen planus has purple polygonal pruritic papules with Wickham striae.
Flashcards
Tap a card to flip it.
What distribution supports eczema?
Flexural itchy plaques support eczema.
What scale supports psoriasis?
Silvery scale on extensor plaques supports psoriasis.
Quick answers
What is the fastest way to tell Eczema from Psoriasis and seborrheic dermatitis?
Eczema is itchy flexural atopy; psoriasis is extensor silvery plaques; seborrheic dermatitis is greasy scale in sebum-rich areas.
What is the key clue for Eczema?
Eczema causes pruritic eczematous dermatitis with flexural involvement, xerosis, atopy, and spongiotic dermatitis.
What is the key clue for Psoriasis and seborrheic dermatitis?
Psoriasis causes well-demarcated plaques with silvery scale on extensor surfaces; seborrheic dermatitis causes greasy scale on scalp, face, and intertriginous areas.
What is the common trap with Eczema vs Psoriasis and seborrheic dermatitis?
All three are chronic scaly rashes, but distribution, scale quality, itch, and atopic history decide. ECZEMA (atopic dermatitis) is intensely PRURITIC, occurs on FLEXURAL surfaces (antecubital and popliteal fossae, neck), with poorly defined erythematous patches, vesicles, weeping, lichenification with chronicity; classic in patients with the atopic triad (asthma, allergic rhinitis, eczema); treat with emollients, topical steroids, topical calcineurin inhibitors (tacrolimus, pimecrolimus), dupilumab for severe. PSORIASIS is well-demarcated salmon-colored plaques with thick SILVERY SCALE on EXTENSOR surfaces (elbows, knees, scalp, sacrum); Auspitz sign (bleeding points on scale removal), Koebner phenomenon (lesions at sites of trauma), nail pitting and oil-drop sign; histology shows parakeratosis and Munro microabscesses; associated with psoriatic arthritis (dactylitis, distal interphalangeal involvement, pencil-in-cup deformity); treat with topical steroids and vitamin D analogs for mild disease; phototherapy or biologics (TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors) for severe. SEBORRHEIC DERMATITIS is greasy YELLOW scale in sebum-rich areas (scalp = dandruff, eyebrows, nasolabial folds, retroauricular, central chest), associated with Malassezia yeast overgrowth; classic in infants (cradle cap) and adults with Parkinson disease, HIV, or stress; treat with antifungal shampoos (ketoconazole) and low-potency steroids.