U01.11.066 Autoimmune blistering skin disorders

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Learning Objectives

Differentiate between Pemphigus Vulgaris (PV) and Bullous Pemphigoid (BP) based on the molecular target (desmosomes vs. hemidesmosomes). Master the histological patterns (reticular vs. linear), clinical signs (Nikolsky sign), and the presence or absence of mucosal involvement.

1. Pathophysiology & Molecular Targets

Both conditions are Type II Hypersensitivity reactions involving IgG antibodies, but they attack different cellular “glues.”

Condition Antibody Target Anatomical Location
Pemphigus Vulgaris IgG vs. Desmoglein 1/3 (Desmosomes). Intraepidermal (within the stratum spinosum).
Bullous Pemphigoid IgG vs. BP180/BP230 (Hemidesmosomes). Subepidermal (at the epidermal-dermal junction).

2. Gross Morphology & Clinical Signs

The depth of the blister determines its stability and whether it affects the delicate mucosal membranes.

Feature Pemphigus Vulgaris (PV) Bullous Pemphigoid (BP)
Blister Type Flaccid (easy to rupture); intraepidermal. Tense (firm); subepidermal.
Nikolsky Sign Positive (skin sloughs with pressure). Negative.
Mucosa Commonly involved (oral ulcers). Usually spared.
Histology Acantholysis; “Row of tombstones”. Subepidermal blister with Eosinophils.

3. Immunofluorescence (IF) Patterns

Direct immunofluorescence reveals the specific “staining” pattern of the IgG antibodies on the biopsy sample.

Condition IF Pattern Visual Description
Pemphigus Vulgaris Reticular (Net-like) Outlines individual keratinocytes like a fishnet.
Bullous Pemphigoid Linear A smooth line at the epidermal-dermal junction.

Activity:

High-Yield Mnemonics:

  • Bullous Pemphigoid: Antibodies are Bullow (Below) the epidermis at the Basement membrane.
  • BP = Benign (less severe) + Brimming with Eosinophils.
  • Pemphigus Vulgaris: Vulgaris is Very bad (potentially fatal) and involves the Vulva/Oral mucosa.
  • Pemphigus = Positive Nikolsky.

Activity