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DR13.1-2 | Vesiculobullous Lesions — Practice Quiz
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A 45-year-old woman presents with painful erosions in the mouth for 3 weeks followed by flaccid skin blisters on the trunk. The blisters rupture easily leaving raw erosions. Nikolsky sign is positive on perilesional skin. Which of the following BEST explains the positive Nikolsky sign?
Correct. In PV, anti-Dsg3 IgG breaks intercellular adhesion suprabasally, leaving the basal cells attached to the dermis like a 'row of tombstones' while the overlying layers slide off — the direct mechanical cause of Nikolsky positivity.
Pemphigus vulgaris is caused by IgG against desmoglein 3 (and desmoglein 1 in widespread disease). Loss of desmosomal adhesion in the suprabasal spinous layer makes the epidermis shear under tangential pressure — the basis of Nikolsky positivity.
Incorrect. The positive Nikolsky sign in pemphigus vulgaris is explained by suprabasal acantholysis from anti-desmoglein 3 IgG, not basement-membrane or IgA-mediated mechanisms.
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A 72-year-old man with no prior skin disease presents with intensely pruritic, large tense blisters on an erythematous base involving the thighs, abdomen, and forearms. Mucous membranes are spared. Nikolsky sign is negative. Direct immunofluorescence of perilesional skin shows linear IgG and C3 at the basement membrane zone. What is the most likely diagnosis?
Correct. All five pillars of bullous pemphigoid are present: elderly age, tense blisters on erythematous base, mucosal sparing, Nikolsky negative, and linear IgG/C3 at the basement membrane zone.
Bullous pemphigoid: elderly patient, tense blisters, pruritus, spared mucosae, Nikolsky negative, linear IgG+C3 at BMZ on DIF. Antigen targets are BP180 and BP230.
Incorrect. The combination of elderly patient + tense blisters + mucosal sparing + Nikolsky negative + linear BMZ immunofluorescence is the classic profile of bullous pemphigoid.
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In pemphigus vulgaris, histopathology of an early intact blister would show:
Correct. Suprabasal acantholysis leaving a 'row of tombstones' (basal cells still attached to BMZ) is the pathognomonic histological feature of pemphigus vulgaris.
PV splits suprabasally: anti-Dsg3 causes acantholysis of spinous cells while the basal layer remains attached — the 'tombstone' pattern. This intra-epidermal location contrasts with BP's subepidermal cleavage.
Incorrect. PV produces a suprabasal (intra-epidermal) split by acantholysis of keratinocytes above the basal layer, leaving basal cells intact as a 'tombstone' row.
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A patient with suspected pemphigus vulgaris has lesions confined ONLY to the oral mucosa (no skin blisters). Which autoantibody pattern would you expect?
Correct. In mucosal-dominant PV, only anti-Dsg3 is detected. Because Dsg1 is present in the skin and compensates, skin blisters do not form unless anti-Dsg1 is also present.
Desmoglein compensation rule: Dsg3 is the dominant adhesion molecule in mucosae. Anti-Dsg3 alone → oral-only disease. Anti-Dsg1+Dsg3 → mucosal + cutaneous disease (more extensive).
Incorrect. The desmoglein compensation theory predicts: anti-Dsg3 alone = oral disease only; anti-Dsg1+Dsg3 = oral + cutaneous disease.
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A 48-year-old man with known pemphigus vulgaris is brought to a primary health centre with multiple ruptured bullae over 30% of body surface area, fever 38.8 °C, and tachycardia. His oral intake has been poor for 4 days. As the primary physician before dermatology referral, which action is MOST immediately appropriate?
Correct. Extensive ruptured bullae with systemic compromise requires immediate supportive care (IV fluids, wound care) and urgent referral — not outpatient follow-up or symptomatic-only treatment.
DR13.2 primary management: extensive blistering = fluid and protein loss risk. Immediate priorities are IV access + fluid replacement, wound protection with non-adherent dressings, pain management, and urgent specialist referral. Do NOT delay resuscitation for confirmatory tests.
Incorrect. A patient with 30% BSA erosions, fever, and dehydration needs immediate IV resuscitation and wound care — outpatient management or diagnostic tests first would be dangerous.
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The Bulla-spread sign (Asboe-Hansen sign) is BEST described as:
Correct. Pressing down on an intact bulla forces fluid laterally under the fragile intra-epidermal plane, enlarging the blister — confirming the level and fragility of the split.
Bulla-spread (Asboe-Hansen) sign: pressing on the top of an intact blister causes it to extend laterally as fluid tracks under the fragile intra-epidermal adhesion. This confirms that epidermal cleavage is ongoing, supporting a diagnosis of pemphigus.
Incorrect. The Asboe-Hansen sign describes lateral extension of an existing intact blister when compressed from above — not distant bulla formation, simple rupture, or erythema spread.
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A 55-year-old woman presents with flaccid blisters on the trunk and erosions in the mouth. You suspect pemphigus vulgaris. Which combination of investigations is most appropriate to confirm the diagnosis?
Correct. H&E shows suprabasal acantholysis; DIF of perilesional (NOT lesional) skin shows the characteristic intercellular (chicken-wire) IgG and C3 pattern, which confirms PV.
Gold-standard confirmation: H&E biopsy (from edge of lesion, including perilesional skin) + DIF of PERILESIONAL skin. DIF shows intercellular IgG/C3 in a chicken-wire pattern. Lesional skin for DIF gives false negatives due to immunoglobulin consumption.
Incorrect. PV is confirmed by H&E (suprabasal acantholysis) + DIF of PERILESIONAL skin (intercellular IgG/C3). Tzanck smear is suggestive only; anti-BP180 ELISA targets a different disease.
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Regarding the proper technique for eliciting Nikolsky sign, which of the following is CORRECT?
Correct. Nikolsky sign = tangential pressure on perilesional normal skin → epidermal shear. This is distinct from the Asboe-Hansen sign (vertical pressure on a blister roof).
Nikolsky sign technique: firm tangential (lateral shearing) pressure with a finger on NORMAL-APPEARING perilesional skin. If the epidermis slides off, the sign is positive. Vertical pressure on a blister describes the Asboe-Hansen sign.
Incorrect. Nikolsky sign requires tangential (lateral shearing) pressure on apparently normal perilesional skin — not vertical pressure on a blister or mucosal rubbing.
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A first-year house officer admits a 67-year-old man with tense blisters. She notes that Nikolsky sign is negative and the blisters have not ruptured spontaneously. She considers bullous pemphigoid. Which clinical feature would MOST support this diagnosis over pemphigus vulgaris?
Correct. The urticarial prodrome — weeks of intense itch with hive-like plaques before blisters appear — is characteristic of bullous pemphigoid and does not occur in pemphigus vulgaris.
BP hallmark: often preceded by pruritic urticarial/eczematous prodrome weeks to months before blisters appear. PV begins with oral erosions. Acantholytic cells on Tzanck smear suggest PV, not BP.
Incorrect. Preceding pruritic urticarial plaques are the hallmark prodrome of bullous pemphigoid. PV typically starts with mucosal erosions, and Tzanck positivity for acantholytic cells favours PV.
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