A woman in her third trimester develops intensely pruritic urticarial plaques and vesicles beginning in periumbilical skin. Biopsy shows a subepidermal blister with eosinophils. Direct immunofluorescence shows a striking linear band at the basement membrane zone composed almost entirely of one immunoreactant. Which immunoreactant is expected?
- A IgA
- B IgG with IgM equally
- C C3, with IgG often undetectable ✓
- D Fibrinogen only
Correct answer: C. C3, with IgG often undetectable
Explanation
Pemphigoid gestationis shares the target antigen BP180 (collagen XVII) with bullous pemphigoid, but the autoantibodies are potent complement fixers, so DIF shows a dominant linear C3 band at the basement membrane zone while IgG is frequently absent or faint by routine methods. IgA linearity would suggest linear IgA bullous dermatosis of childhood/adulthood, and fibrinogen alone is nonspecific.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.