Pemphigus Foliaceus

Overview & Pathogenesis - Leafy Skin Split

• Pemphigus Foliaceus (PF): A chronic, superficial autoimmune blistering disease affecting the skin.
• Core Pathogenesis:
  • Autoantibodies (IgG, often IgG4) target Desmoglein 1 (DSG1), a keratinocyte adhesion molecule.
  • Leads to acantholysis (separation of keratinocytes).
  • Results in intraepidermal split within the superficial epidermis (subcorneal or upper granular layer).
  • 📌 Foliaceus = Fragile, Flakes (superficial, "leaf-like" scales).

⭐ Pemphigus foliaceus is the most common autoimmune blistering disease in certain endemic regions of Brazil (Fogo Selvagem).

Clinical Features - Scaly Crusty Rash

• Morphology:
  • Superficial, fragile blisters (often ruptured, rarely seen intact).
  • Leads to scaly, crusted erosions.
  • Characteristic "cornflake" like scales.
  • Well-demarcated lesions.
• Distribution:
  • Primarily affects seborrheic areas:
    • Scalp (often initial site)
    • Face (malar region, forehead)
    • Chest (V-area)
    • Upper back
• Mucous Membranes: Typically spared (key differentiator from Pemphigus Vulgaris).
• Symptoms:
  • Pruritus (itching) is common and can be intense.
  • Burning sensation may occur.
• Variants:
  • Fogo Selvagem (Endemic Pemphigus Foliaceus): Brazil, rural areas.
  • Pemphigus Erythematosus (Senear-Usher Syndrome): Overlap with lupus erythematosus; facial lesions, +ANA.

⭐ Nikolsky sign is often positive in Pemphigus Foliaceus, though blisters are very superficial.

Diagnosis - Spotting the Split

Key investigations aim to identify the specific level of epidermal split and the presence of pathogenic autoantibodies:

• Skin Biopsy: Crucial for diagnosis.
  • Lesional skin (Histopathology - HPE): Shows characteristic subcorneal or intragranular acantholysis (epidermal cell separation).
  • Perilesional skin (Direct Immunofluorescence - DIF): Gold standard; reveals intercellular IgG and C3 deposition in the superficial epidermis, creating a "chicken-wire" pattern.

    ⭐ Direct immunofluorescence showing intercellular IgG deposition in the superficial epidermis is key for diagnosis.

• Serum Tests:
  • Indirect Immunofluorescence (IIF): Detects circulating anti-Desmoglein 1 (anti-DSG1) IgG autoantibodies.
  • ELISA (Enzyme-Linked Immunosorbent Assay): Confirms presence and quantifies anti-DSG1 antibodies; useful for diagnosis and monitoring disease activity.
• Tzanck Smear:
  • Rapid test showing acantholytic cells (Tzanck cells); less specific but can be suggestive.

DDx & Management - Calm the Chaos

Differential Diagnosis:

⭐ Unlike Pemphigus Vulgaris, Pemphigus Foliaceus generally has a better prognosis and lower mortality rate.

High‑Yield Points - ⚡ Biggest Takeaways

• Superficial autoimmune blistering disease; targets Desmoglein 1 (DSG1).
• Histopathology: subcorneal split with acantholytic cells in the upper epidermis.
• Clinical: crusted, scaly erosions on seborrheic areas (face, scalp, chest); mucosa is spared.
• Nikolsky sign is typically positive.
• DIF: intercellular IgG and C3 deposition in a "fish-net" or "chicken-wire" pattern in superficial epidermis.
• Endemic form in South America is Fogo Selvagem; associated with black fly bites (Simulium).