Bullous Pemphigoid

Bullous Pemphigoid: Overview & Patho - Elder Itch & Attack

• Autoimmune disease: large, tense subepidermal blisters.
• Affects elderly (>60 yrs); often preceded by intense pruritus (📌 "Elder Itch").
• Pathophysiology ("Attack"):
  • Autoantibodies (IgG, IgE) target hemidesmosome proteins:
    • BPAG1 (BP230) - intracellular.
    • BPAG2 (BP180/Type XVII collagen) - transmembrane.
  • Immune cascade: Complement activation → eosinophil/mast cell recruitment → protease release → split at lamina lucida of basement membrane zone.

⭐ Most common autoimmune blistering disease in the elderly.

Bullous Pemphigoid: Clinical Canvas - Tense Bubbles Appear

• Onset: Typically elderly, >60 years.
• Prodrome: Intense pruritus, often preceding skin lesions by weeks/months; may have urticarial plaques.
• Lesions: Hallmark is tense, large bullae (1-4 cm) filled with clear or serosanguinous fluid.
  • Arise on erythematous, urticarial, or normal-appearing skin.
• Distribution: Predilection for flexural areas (axillae, groin, abdomen, inner thighs), trunk, and limbs.
• Mucosal Involvement: Oral lesions in 10-30% of cases; typically less severe and extensive than in Pemphigus Vulgaris.
• Healing: Usually without scarring, but post-inflammatory hyperpigmentation is common.

⭐ Nikolsky sign is typically negative, distinguishing it from Pemphigus Vulgaris where it's often positive (skin surface does not shear off easily when rubbed).

Bullous Pemphigoid: Diagnostic Deep Dive - Unmasking BP

• Skin Biopsy (H&E): Subepidermal blister, prominent eosinophils.
• Direct Immunofluorescence (DIF): Linear deposition of IgG & C3 along dermoepidermal junction (DEJ).

  ⭐ Direct Immunofluorescence (DIF) showing linear deposition of IgG and/or C3 along the dermoepidermal junction is the gold standard.

• Indirect Immunofluorescence (IIF): Circulating IgG anti-BMZ antibodies; "roof" pattern on salt-split skin.
• ELISA: Detects autoantibodies against BPAG1 (BP230) & BPAG2 (BP180, esp. NC16A domain).

Bullous Pemphigoid: Differential Diagnosis - Ruling Out Lookalikes

• Pemphigus Vulgaris (PV): Flaccid blisters, intraepidermal, +Nikolsky. Oral lesions common.
• Epidermolysis Bullosa Acquisita (EBA): Subepidermal, trauma-prone sites, scarring. Salt-split skin: IgG on dermal side.
• Linear IgA Bullous Dermatosis (LABD): Subepidermal, "string of pearls" appearance. Linear IgA at BMZ.
• Dermatitis Herpetiformis (DH): Grouped pruritic vesicles (extensors). Granular IgA deposits.

⭐ Key differentiator from Pemphigus Vulgaris: BP features subepidermal blisters targeting hemidesmosomes (BPAG1/BP230, BPAG2/BP180). PV shows intraepidermal blisters targeting desmosomes (Desmoglein 1/3).

Bullous Pemphigoid: Treatment Tactics - Quelling the Blisters

• Primary Goals: Control disease, heal lesions, reduce pruritus, minimize therapy toxicity.
• Management Approach:

⭐ For generalized bullous pemphigoid, systemic corticosteroids (e.g., prednisolone 0.5-1 mg/kg/day) are the mainstay of treatment, often combined with steroid-sparing agents.

• Other Options/Adjuvants:
  • Tetracycline (e.g., Doxycycline) + Niacinamide (📌 "TetraNi"): Mild cases or adjuvant.
• Supportive Care: Wound management, antihistamines for itching.

High‑Yield Points - ⚡ Biggest Takeaways

• Elderly patients are most commonly affected; it's an autoimmune subepidermal blistering disease.
• Presents with tense, large bullae on erythematous or urticarial plaques; often preceded by intense pruritus.
• Nikolsky sign is characteristically negative, distinguishing it from Pemphigus.
• Direct Immunofluorescence (DIF) shows linear IgG and C3 deposits at the dermoepidermal junction (DEJ).
• Autoantibodies target hemidesmosomal proteins BPAG1 (BP230) and BPAG2 (BP180/Type XVII collagen).
• Oral lesions are present in only 10-30% of cases, less common than Pemphigus Vulgaris.