Summary

Bullous Pemphigoid (BP) is the most common autoimmune blistering disease, primarily affecting the elderly (>70 years). It is caused by autoantibodies (IgG) targeting hemidesmosomal antigens (BP180 and BP230) at the dermal-epidermal junction, leading to subepidermal blister formation. The clinical hallmark is tense, fluid-filled blisters on erythematous or urticarial skin, typically on the limbs, trunk, and flexures. Unlike Pemphigus Vulgaris (which has flaccid blisters), BP blisters are difficult to rupture and the Nikolsky sign is negative. Mucosal involvement is rare. Treatment focuses on reducing inflammation with topical or systemic corticosteroids, with steroid-sparing agents (Doxycycline, Methotrexate, Azathioprine) for severe or refractory disease.

Key Facts

• Epidemiology: Most common autoimmune blistering disease. Peak age >70 years.
• Antibodies: Anti-BP180 (NC16A domain) and Anti-BP230 IgG.
• Blister Type: Subepidermal (Below epidermis). TENSE (Hard to rupture).
• Nikolsky Sign: Negative (Skin does not shear with lateral pressure – epidermis is intact).
• Mucosal Involvement: Rare (~10-30% minor oral involvement).
• Treatment (Mild/Localised): Potent Topical Steroids (Clobetasol/Dermovate).
• Treatment (Severe/Widespread): Oral Prednisolone +/- Steroid-Sparing Agents.

Clinical Pearls

"Tense Blisters in the Elderly = Think Pemphigoid": BP blisters are characteristically tense (difficult to pop). This is because the roof is intact epidermis.

"Nikolsky Negative Pemphigoid, Nikolsky Positive Pemphigus": The Nikolsky sign helps differentiate. In Pemphigus (intraepidermal split), skin shears easily.

"DPP-4 Inhibitors Can Cause BP": Drug-induced BP is increasingly recognised. Check for Gliptins (Sitagliptin, Linagliptin, etc.).

"Potent Topical Steroids Work": For localised/mild BP, potent topical steroids (Clobetasol) can be as effective as oral steroids with fewer systemic side effects.

Why This Matters Clinically

BP predominantly affects elderly, frail patients who tolerate systemic steroids poorly. Recognising BP early, using topical steroids where appropriate, and managing infection risk is critical for patient outcomes.

Key Examination Findings

Differential Diagnosis

• Remission: Most achieve remission within 1-5 years.
• Relapse: Common. May need retreatment.
• Mortality: Elevated (~10-40% at 1 year), primarily due to age, frailty, infection, and steroid toxicity. Not the disease itself.
• Drug-Induced BP: Often remits on drug withdrawal.

Drug-Induced BP: DPP-4 Inhibitors (Gliptins)

Increasingly recognised cause.

Key Points:

• Onset: Months to years after starting drug.
• May present atypically (Non-inflammatory, Less urticarial).
• Management: Stop the Gliptin. May remit on withdrawal.
• If ongoing: Treat as standard BP.

Non-Bullous Pemphigoid

A diagnostic challenge.

Special Populations

Prognosis Factors

Monitoring on Treatment

Common Clinical Pitfalls

Key Guidelines

Evidence Highlights

Scenario 1:

• Stem: An 80-year-old man presents with intensely itchy, tense blisters on his arms and trunk. Nikolsky sign is negative. Skin biopsy shows subepidermal blistering with eosinophils. DIF shows linear IgG and C3 at the basement membrane zone. What is the diagnosis?
• Answer: Bullous Pemphigoid.

Scenario 2:

• Stem: How do the blisters in Bullous Pemphigoid differ from those in Pemphigus Vulgaris?
• Answer: BP blisters are tense (Subepidermal, roof is intact epidermis). Pemphigus blisters are flaccid (Intraepidermal, fragile). Nikolsky is negative in BP, positive in Pemphigus.

Scenario 3:

• Stem: An 85-year-old woman with type 2 diabetes on Sitagliptin develops widespread blistering. What should you consider?
• Answer: Drug-induced Bullous Pemphigoid (DPP-4 inhibitor associated). Stop Sitagliptin. May remit on drug withdrawal.

Scenario 4:

• Stem: What is the first-line treatment for localised Bullous Pemphigoid?
• Answer: Potent Topical Corticosteroid (Clobetasol Propionate 0.05% / Dermovate) applied twice daily.

What is Bullous Pemphigoid?

Bullous Pemphigoid (BP) is a skin condition where the body's immune system mistakenly attacks part of the skin, causing large, itchy blisters to form.

Who gets it?

It mainly affects older people, usually over 70. It is not contagious – you cannot catch it from someone else.

What are the symptoms?

• Large, tense blisters (hard to pop) on the arms, legs, and body.
• Severe itching.
• Red, raised patches that may appear before blisters.

How is it treated?

• Steroid creams: Applied directly to the blisters. Very effective.
• Steroid tablets: If the disease is widespread.
• Other medicines: To reduce the need for steroids.

Will it go away?

Most people get better within a few years, but it can come back. The main challenge is managing it safely, especially in older people.

Key Counselling Points

1. It's Treatable: "This condition can be controlled with treatment."
2. Watch for Infection: "If your skin becomes hot, red, or smelly, or you feel unwell, contact us immediately."
3. Steroid Creams Work: "Strong steroid creams are very effective and safer than tablets for many people."
4. Drug-Induced BP: "Tell us all your medications – some diabetes tablets can cause this."

Pemphigoid Gestationis (Herpes Gestationis)

A special variant – occurs in pregnancy.

Patient FAQs

Key Counselling Points (Expanded)

1. It's Treatable: "Bullous Pemphigoid is a manageable condition. Most people achieve remission."
2. Infection is the Main Risk: "Watch for signs of infection – redness spreading, fever, pus. This needs urgent treatment."
3. Apply Creams Generously: "For topical steroids to work, you need to use enough. 30-40g/day is normal for widespread disease."
4. Drug Review: "Please bring a list of all your medications. Some drugs can trigger or worsen BP."
5. Steroid Side Effects: "If you're on steroid tablets, we'll monitor your blood pressure, blood sugar, and bones."
6. Follow-Up is Important: "Regular reviews help us adjust treatment and catch problems early."

When to Seek Urgent Help

• Walter Lever (1953): First clearly distinguished Bullous Pemphigoid from Pemphigus Vulgaris based on histology (Subepidermal vs Intraepidermal).
• Jordon et al. (1967): Identified basement membrane zone as the target using immunofluorescence.
• BP180 & BP230: Target antigens identified in the 1980s-90s.