Pemphigus vs Pemphigoid — MRCP Part 1 Guide

TL;DR

For MRCP Part 1, distinguishing pemphigus vs pemphigoid is a classic dermatology question that tests clinical pattern recognition and immunopathology. Pemphigus causes intraepidermal blistering due to antibodies against desmogleins, leading to fragile blisters and mucosal disease. Bullous pemphigoid produces subepidermal blistering from antibodies against hemidesmosomes, resulting in tense bullae in older adults. Mastering these contrasts helps quickly identify the diagnosis in exam scenarios.

Bullous Disorders: Pemphigus vs Pemphigoid (MRCP Part 1)

Why this matters

Autoimmune blistering diseases are repeatedly tested in MRCP Part 1 dermatology questions because they integrate several examinable themes:

• Immunology

• Clinical dermatology

• Histopathology

• Pattern recognition

In exam questions, candidates are often given a short clinical vignette followed by clues such as blister type, mucosal involvement, age, or biopsy findings. Recognising the correct pattern allows rapid diagnosis.

If you are revising dermatology for the exam, review the MRCP Part 1 overview and practise scenario-based questions using Free MRCP MCQs.

Core differences between pemphigus and pemphigoid

A high-yield strategy for revision is to memorise the classic contrast table.

Feature	Pemphigus vulgaris	Bullous pemphigoid
Level of blister	Intraepidermal	Subepidermal
Target antigen	Desmoglein 1 & 3	BP180 (type XVII collagen), BP230
Autoantibody type	IgG against desmosomes	IgG against hemidesmosomes
Blister type	Flaccid	Tense
Mucosal involvement	Common	Rare
Nikolsky sign	Positive	Usually negative
Typical age group	Middle-aged adults	Elderly
Histology	Acantholysis	Subepidermal split
Immunofluorescence	Intercellular “fish-net” IgG	Linear IgG at basement membrane
Clinical severity	Potentially severe	Often milder

This table summarises the most exam-relevant features.

The five most tested concepts in MRCP Part 1

1. Immunopathology

Understanding the target proteins explains the disease.

Pemphigus vulgaris

• Autoantibodies against desmoglein proteins

• Desmogleins are part of desmosomes, which connect keratinocytes

• Loss of adhesion causes acantholysis

Result: intraepidermal blister formation

Bullous pemphigoid

• Autoantibodies against BP180 and BP230

• These proteins form hemidesmosomes, anchoring epidermis to dermis

Result: subepidermal blister

Helpful exam memory rule:

Desmosomes → epidermis → pemphigusHemidesmosomes → basement membrane → pemphigoid

Authoritative background information can be reviewed via the British Association of Dermatologists and NHS overview of bullous pemphigoid.

2. Clinical presentation

Clinical features are often the first clue in exam questions.

Pemphigus vulgaris

Common findings include:

• Painful oral ulcers

• Flaccid skin blisters

• Erosions after blister rupture

• Positive Nikolsky sign

In many patients, oral disease appears first.

Bullous pemphigoid

Typical presentation includes:

• Elderly patient

• Intense itching

• Tense bullae

• Often preceded by urticarial plaques

Mucosal involvement is uncommon.

3. Histology and immunofluorescence

Biopsy findings are another favourite MRCP testing area.

Pemphigus vulgaris

Histology:

• Intraepidermal cleft

• Acantholysis

Direct immunofluorescence:

• Intercellular IgG deposition

• Often described as a “fish-net pattern”

Bullous pemphigoid

Histology:

• Subepidermal blister

• Eosinophilic infiltrate

Direct immunofluorescence:

• Linear IgG deposition along the basement membrane

Further details on diagnostic testing can be found in dermatology references such as DermNet NZ.

4. Drug triggers and associations

Bullous pemphigoid may be triggered by medications. MRCP questions sometimes include this detail.

Reported drug associations include:

• Loop diuretics

• Penicillamine

• Antibiotics

• Immune checkpoint inhibitors

In an exam vignette, new medication followed by pruritic tense bullae in an elderly patient should raise suspicion of bullous pemphigoid.

5. Management principles

Although MRCP Part 1 focuses more on diagnosis, basic treatment principles are sometimes tested.

Pemphigus vulgaris

Management may include:

• Systemic corticosteroids

• Immunosuppressants (azathioprine or mycophenolate)

• Rituximab for refractory disease

Bullous pemphigoid

Management typically involves:

• Potent topical corticosteroids

• Oral steroids if widespread

• Immunosuppressive therapy in severe cases

Structured revision of dermatology topics can be reinforced through MRCP lectures.

Ten rapid revision points

Use this quick checklist before the exam:

1. Pemphigus → intraepidermal blister

2. Pemphigoid → subepidermal blister

3. Pemphigus antibodies target desmogleins

4. Pemphigoid antibodies target hemidesmosomes

5. Pemphigus blisters are flaccid

6. Pemphigoid blisters are tense

7. Pemphigus frequently involves oral mucosa

8. Pemphigoid occurs mainly in the elderly

9. Immunofluorescence pattern: fish-net vs linear

10. Nikolsky sign usually positive in pemphigus

Mini-case (MRCP style)

A 72-year-old woman presents with a three-week history of severe itching followed by the appearance of multiple tense blisters on her abdomen and thighs. The oral mucosa is normal. A skin biopsy shows a subepidermal blister with eosinophils.

What is the most likely diagnosis?

A. Pemphigus vulgarisB. Bullous pemphigoidC. Dermatitis herpetiformisD. Linear IgA diseaseE. Stevens-Johnson syndrome

Correct answer: B. Bullous pemphigoid

Explanation:

The key clues are:

• Elderly age group

• Pruritic eruption

• Tense bullae

• Subepidermal split with eosinophils

• Absence of mucosal lesions

These findings strongly support bullous pemphigoid.

You can practise similar clinical questions using Free MRCP MCQs or simulate exam conditions with a mock test.

Common pitfalls (exam traps)

1. Confusing blister tension Flaccid blisters suggest pemphigus, not pemphigoid.

2. Ignoring age clues Bullous pemphigoid typically affects older adults.

3. Misinterpreting biopsy descriptions Subepidermal blister strongly indicates pemphigoid.

4. Forgetting mucosal involvement Oral lesions are common in pemphigus vulgaris.

5. Mixing up immunofluorescence patterns Intercellular = pemphigus; linear basement membrane = pemphigoid.

Study-tip checklist for MRCP Part 1

To revise autoimmune blistering diseases efficiently:

Step 1 — Understand skin structure

Learn:

• Desmosomes

• Hemidesmosomes

• Basement membrane

Step 2 — Link structure to disease

• Desmosomes → pemphigus

• Hemidesmosomes → pemphigoid

Step 3 — Memorise the comparison table

This covers multiple exam questions at once.

Step 4 — Practise clinical scenarios

Use MCQ practice and timed revision sessions.

Step 5 — Use visual learning

Dermatology questions often rely on image recognition.

FAQs

What is the key difference between pemphigus and pemphigoid?

Pemphigus causes intraepidermal blistering due to antibodies against desmogleins, producing fragile blisters and mucosal lesions. Pemphigoid causes subepidermal blistering due to antibodies against basement membrane proteins, leading to tense bullae.

Is Nikolsky sign positive in bullous pemphigoid?

Usually not. Nikolsky sign is typically positive in pemphigus vulgaris, where superficial epidermal adhesion is lost.

Which age group is most affected by bullous pemphigoid?

Bullous pemphigoid mainly affects elderly individuals, often over the age of 60–70.

How are autoimmune blistering diseases diagnosed?

Diagnosis usually involves skin biopsy and direct immunofluorescence, which demonstrate characteristic antibody deposition patterns.

Why is pemphigus potentially more severe than pemphigoid?

Pemphigus causes intraepidermal loss of adhesion, leading to widespread skin breakdown, infection risk, and fluid loss if untreated.

Ready to start?

Dermatology questions in MRCP Part 1 often reward candidates who recognise clinical patterns quickly. Review the full exam structure in the MRCP Part 1 overview, practise scenario-based questions with Free MRCP MCQs, and test your readiness with a mock exam.

Sources

• MRCP(UK) Examination Blueprint

• British Association of Dermatologists — https://www.bad.org.uk

• NHS: Bullous pemphigoid — https://www.nhs.uk/conditions/bullous-pemphigoid/

• DermNet NZ: Pemphigus vulgaris — https://dermnetnz.org/topics/pemphigus-vulgaris

• Rook’s Textbook of Dermatology