Image MCQ Walkthrough: Psoriasis vs Eczema — Visual Differentiation for NEET PG

Version 1.0 — Published April 2026

Clinical image presentation

A 35-year-old male bank employee presents to the dermatology OPD with multiple raised, reddish patches on both elbows and knees that have been present for 8 months. He reports that the patches have gradually increased in size. He describes moderate itching, worsening in winter months. He noticed that a scratch from his cat 3 weeks ago has developed a similar raised patch along the scratch line. He has no history of asthma, allergic rhinitis, or atopic dermatitis in childhood.

Examination findings:

On inspection of the elbows and knees, the following features are visible:

• Well-demarcated, erythematous plaques with sharply defined borders
• Thick, silvery-white scales covering the surface of the plaques
• Plaques are elevated (palpable) with a salmon-pink base
• Linear plaque along a scratch mark on the forearm (isomorphic response)
• Bilateral and roughly symmetrical distribution
• No vesicles, no weeping, no excoriation marks

On gentle scraping of the scale with a glass slide:

• Successive layers of silvery scale separate like candle grease (candle grease sign)
• After complete scale removal, a thin, shiny membrane is visible (Auspitz last membrane)
• Removal of this membrane reveals pinpoint bleeding spots (Auspitz sign)

MCQ question as it appears in NEET PG

A 35-year-old male presents with well-demarcated, erythematous plaques covered with silvery scales on both elbows and knees for 8 months. On removing the scales, pinpoint bleeding is observed. New similar lesions have appeared at the site of a recent scratch. The most likely diagnosis is:

• (a) Atopic dermatitis
• (b) Psoriasis vulgaris
• (c) Seborrheic dermatitis
• (d) Lichen planus

Take a moment to work through this before reading the analysis below.

Step-by-step visual analysis

Systematic dermatological image reading prevents the common error of pattern-matching on color alone. Use this 5-step approach for every dermatology image MCQ:

Step 1: Assess the border

The plaques have sharply defined, well-demarcated borders — you can clearly see where the lesion ends and normal skin begins. This is a hallmark of psoriasis. In contrast, eczema has ill-defined, gradually blending borders that merge with surrounding normal skin.

Why this matters: Border definition alone narrows the differential significantly. Well-demarcated plaques point to psoriasis, lichen planus, or fungal infection. Ill-defined patches point to eczema, seborrheic dermatitis, or early mycosis fungoides.

Step 2: Examine the scale

The scales are thick, silvery-white, and adherent. They form multiple layers (micaceous scale) that separate like candle wax (candle grease sign/Grattage test). This is characteristic of psoriasis.

Compare with:

• Eczema — fine, dry scaling or no visible scale; may show weeping/crusting in acute phase
• Seborrheic dermatitis — greasy, yellowish scales on an erythematous base
• Lichen planus — no scale; flat-topped violaceous papules with Wickham striae (fine white lines)
• Pityriasis rosea — collarette scale (peripheral scaling with clear center)

Step 3: Check the distribution pattern

The lesions are on extensor surfaces (elbows and knees) — the classic psoriasis distribution. Other psoriasis-favored sites: scalp (extending beyond the hairline), sacral area, umbilicus, nails.

Step 4: Identify pathognomonic signs

Three signs are virtually diagnostic of psoriasis:

1. Auspitz sign — pinpoint bleeding on scale removal. Caused by suprapapillary thinning of the epidermis and dilated capillary loops in elongated dermal papillae. This sign is positive in the vignette.

2. Koebner phenomenon (isomorphic response) — new psoriatic lesions at sites of trauma. The vignette describes a new plaque along a scratch mark. This occurs in active disease, typically 10-14 days after trauma. Also seen in lichen planus, vitiligo, and warts — but combined with silvery scales and extensor distribution, it confirms psoriasis.

3. Candle grease sign (Grattage test) — scales separate in layers like candle wax on scraping.

Step 5: Rule out differentials

• (a) Atopic dermatitis: Wrong. Atopic dermatitis shows ill-defined patches, flexural distribution, intense pruritus with excoriations, and a personal/family history of atopy (asthma, allergic rhinitis). No silvery scales, no Auspitz sign. The patient has no atopic history.
• (c) Seborrheic dermatitis: Wrong. Greasy yellowish scales, not silvery. Affects seborrheic areas (scalp, nasolabial folds, eyebrows, chest). Does not show Auspitz sign or Koebner phenomenon.
• (d) Lichen planus: Wrong. Flat-topped, violaceous papules with Wickham striae. The 6 Ps: Pruritic, Purple, Polygonal, Planar, Papules, Plaques. Affects wrists, ankles, oral mucosa, genitalia. No silvery scales.

Answer: (b) Psoriasis vulgaris. The well-demarcated plaques with silvery scales on extensors, positive Auspitz sign, and Koebner phenomenon are pathognomonic.

Detailed visual comparison: psoriasis vs eczema

The following table is the core differentiator that NEET PG image MCQs test:

Similar patterns comparison table

Frequently asked questions

What is the Auspitz sign and which condition shows it?

The Auspitz sign is the appearance of pinpoint bleeding when silvery scales are removed from a psoriatic plaque. It occurs because the psoriatic epidermis is thin above the dermal papillae (suprapapillary thinning), and removing the scales exposes dilated capillary loops. This sign is pathognomonic for psoriasis and does not occur in eczema.

What is the Koebner phenomenon?

The Koebner phenomenon (isomorphic response) is the development of new lesions at sites of skin trauma. In psoriasis, new plaques appear along scratch marks or scars, typically 10-14 days after trauma. Other conditions showing this include lichen planus, vitiligo, and warts.

How do I differentiate psoriasis from eczema on a clinical image?

Five visual keys: border definition (sharp in psoriasis, blurred in eczema), scale type (silvery in psoriasis, fine/absent in eczema), surface (dry in psoriasis, vesicular/lichenified in eczema), distribution (extensors vs flexures), and associated signs (Auspitz sign in psoriasis, intense pruritus in eczema).

What is the histopathology of psoriasis vs eczema?

Psoriasis: regular acanthosis, suprapapillary thinning, Munro microabscesses, parakeratosis, absent granular layer. Eczema: spongiosis (intercellular edema), irregular acanthosis, preserved granular layer. The Munro microabscess is specific to psoriasis.

What are the types of psoriasis tested in NEET PG?

Chronic plaque (most common, 80-90%), guttate (post-streptococcal), pustular (Von Zumbusch), erythrodermic (above 90% BSA), inverse (flexural), nail psoriasis, and psoriatic arthritis (asymmetric, DIP joints, dactylitis).

What is the treatment approach for psoriasis vs eczema?

Psoriasis: topical steroids + vitamin D analogs, phototherapy (NB-UVB), systemic agents (methotrexate, cyclosporine), biologics (anti-TNF, anti-IL17/23). Eczema: emollients (cornerstone), topical steroids for flares, calcineurin inhibitors for face, antihistamines, dupilumab for severe atopic dermatitis.

For comprehensive dermatology MCQ practice, use the Medicine subject page — dermatology questions fall under Medicine in NEET PG. For another image-based walkthrough, see our ECG interpretation guide for STEMI.

Start practicing dermatology MCQs today — the pattern recognition you build now is the recognition you will apply on exam day. Start with 15 free dermatology MCQs. Want unlimited AI-powered image MCQs with visual explanations? Explore NEETPGAI Pro.

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Written by: NEETPGAI Editorial Team Reviewed by: NEETPGAI Medical Advisory Board Last reviewed: April 2026

This article is reviewed by qualified medical professionals for clinical accuracy and exam relevance. For corrections or updates, contact the editorial team.