Which single histopathological feature best distinguishes bullous pemphigoid from pemphigus vulgaris?

Explanation

## Histopathological Distinction Between BP and PV ### Bullous Pemphigoid (BP) — Subepidermal Blister **Key Point:** The hallmark of BP is a **subepidermal blister** with an **intact basal layer** of keratinocytes. The blister forms at the dermal–epidermal junction (DEJ), specifically at the level of the hemidesmosomes. ### Pemphigus Vulgaris (PV) — Intraepidermal Acantholysis **Key Point:** PV is characterized by **intraepidermal acantholysis** (loss of cell-to-cell adhesion) with formation of a **suprabasal cleft**. The basal cells remain attached to the basement membrane but are separated from the overlying epidermis. ### Comparative Table | Feature | Bullous Pemphigoid | Pemphigus Vulgaris | | --- | --- | --- | | **Blister location** | Subepidermal (DEJ) | Intraepidermal (suprabasal) | | **Basal layer** | Intact, attached to dermis | Intact but separated from acantholytic cells | | **Acantholysis** | Absent | Present (loss of desmoglein-3) | | **Inflammatory infiltrate** | Mixed (lymphocytes, eosinophils) | Variable (often sparse in early lesions) | | **Roof of blister** | Thin epidermis | Thick epidermis | ### Immunofluorescence Correlation **High-Yield:** - **BP:** Linear IgG and C3 along the basement membrane zone (BMZ) - **PV:** Intercellular IgG ("tombstone" pattern) in the epidermis **Clinical Pearl:** The subepidermal location in BP makes blisters more fragile and prone to rupture, whereas the thicker roof in PV blisters makes them more resistant to trauma. ### Why This Matters **Tip:** On a histology slide, the single most discriminating feature is the **location of the blister** — if you see the blister *below* the basal layer (subepidermal), think BP; if *above* the basal layer (intraepidermal), think PV.