A 3-year-old boy presents with a 2-week history of recurrent blistering lesions on his lower abdomen and inner thighs. Examination reveals tense, fluid-filled bullae arranged in annular clusters around central crusts, producing a characteristic "string of pearls" appearance as marked **A** in the diagram. Direct immunofluorescence of perilesional skin shows linear IgA deposition along the basement membrane zone. Which of the following best describes the pathogenic mechanism underlying this clinical presentation?

Question

Accepted Answer

B. IgA autoantibodies targeting basement membrane components (LAD-1, LABD97, or BP180) causing subepidermal blister formation. ## Why IgA autoantibodies targeting basement membrane components is right

Linear IgA Bullous Dermatosis (LABD), also called Chronic Bullous Disease of Childhood (CBDC) when presenting in children aged 2–5 years, is defined by IgA autoantibodies directed against basement membrane zone antigens—most commonly LAD-1 and LABD97 (proteolytic fragments of BP180/collagen XVII), and less frequently BP230 or type VII collagen. These IgA antibodies bind to the dermoepidermal junction, activate complement and recruit neutrophils, causing subepidermal blister formation. The characteristic "string of pearls" or "crown of jewels" appearance (option A) is the clinical hallmark of this disease and directly reflects the subepidermal blistering pathology. Direct immunofluorescence showing linear IgA at the basement membrane zone is the defining diagnostic finding (Bolognia Dermatology 5e; Fitzpatrick's Dermatology 9e).

## Why each distractor is wrong

- **IgG autoantibodies against desmoglein 3**: This describes pemphigus vulgaris, which causes intraepidermal acantholytic blistering (flaccid bullae), not subepidermal blistering. Desmoglein antibodies are not involved in LABD.
- **IgE-mediated mast cell degranulation**: This mechanism is seen in dermatitis herpetiformis and other IgE-mediated reactions, which present with grouped vesicles at pressure-prone sites (elbows, knees) rather than annular bullae on the lower abdomen and thighs.
- **IgM immune complexes in dermal vasculitis**: This describes vasculitic bullous diseases such as leukocytoclastic vasculitis, which present with palpable purpura and hemorrhagic lesions, not tense annular bullae with the string-of-pearls sign.

**High-Yield:** Linear IgA at the basement membrane zone on DIF = LABD; the "string of pearls" sign in a young child is pathognomonic for the childhood form (CBDC).

[cite: Bolognia Dermatology 5e; Fitzpatrick's Dermatology 9e]

Answer

A. IgE-mediated mast cell degranulation triggering grouped vesicles at pressure-prone sites

Answer

C. IgG autoantibodies against desmoglein 3 causing acantholysis and intraepidermal blister formation

Answer

D. IgM immune complexes depositing in dermal vessels causing vasculitis and bullae formation

Explanation

Why IgA autoantibodies targeting basement membrane components is right

Why each distractor is wrong

Practice similar questions