What are the pathophysiology, risk factors, clinical features, and diagnostic criteria of pemphigus?

Pemphigus: Comprehensive Overview

1. Pathophysiology

Pemphigus is an acquired autoimmune disease where IgG antibodies target desmosomal proteins, specifically desmoglein 3 (and desmoglein 1 in 50-60% of cases), causing intraepithelial acantholysis and mucocutaneous blistering 1.

The antibody profile determines clinical phenotype:

• Desmoglein 3 antibodies alone → predominantly mucosal disease
• Desmoglein 3 + desmoglein 1 antibodies → mucocutaneous disease (more severe, slower treatment response, less likely to achieve remission)

The pathogenic antibodies belong to the IgG class and disrupt the intercellular adhesion between keratinocytes by targeting cadherin family proteins in desmosomes, leading to suprabasal acantholysis and blister formation 1, 2.

2. Risk Factors and Triggers

Demographic Factors

• Peak incidence: Third to sixth decades of life 1
• Gender: Higher prevalence in females (based on pregnancy data suggesting hormonal influence) 3

Environmental and Occupational Exposures

Exposure to pesticides and metal vapor significantly increases pemphigus risk 3. Key findings include:

• Pesticide exposure: Highest among Bulgarian patients, followed by Israeli patients
• Occupational metal vapor exposure: Associated with increased disease risk
• Gardening materials: Increased exposure correlates with disease development

Protective Factors

• Smoking: Paradoxically shows protective effect (ex-smokers and current smokers have lower risk than never-smokers), possibly through immune modulation and antiestrogenic effects 3

Other Associations

• Drug exposure: Certain medications can trigger disease 4
• Pregnancy: Higher number of pregnancies in pemphigus patients suggests estrogenic contribution 3
• Genetic background: Necessary but requires environmental triggers for disease manifestation 4

3. Clinical Features and Signs

Initial Presentation

The oral mucosa is the first site of involvement in the majority of cases, with diagnostic delay being very common when confined to oral mucosa 1.

Disease Patterns

Mucosal-only disease (23% of patients):

• Oral erosions predominate
• Lower mortality (1-17%)
• Better prognosis, faster treatment response
• More likely to achieve remission off-treatment

Mucocutaneous disease (27% of patients):

• Skin and mucous membrane involvement
• Higher mortality (8-42%)
• More severe disease course
• Slower treatment response, less likely to achieve remission

Skin-only disease (50% of patients):

• May eventually develop oral involvement
• Average lag period of 4 months from oral to skin involvement 1

Key Clinical Signs

• Mucocutaneous erosions and blisters (hallmark finding)
• Oral erosions: Eventually occur in most cases, even if initially presenting with cutaneous lesions
• Suprabasal blistering: Leads to flaccid bullae that rupture easily
• Nikolsky sign: Often positive (though not specific)

Geographic Variations

Bulgarian patients show less frequent oral involvement (66%) compared to Israeli (92%) and Italian patients (83%) 3.

4. Diagnosis

Gold Standard Diagnostic Approach

Direct immunofluorescence (DIF) remains the gold-standard diagnostic investigation, showing characteristic IgG and/or complement deposition on keratinocyte cell surfaces 1.

Biopsy Protocol

For patients with skin lesions:

• Histology: Perilesional skin biopsy showing suprabasal acantholysis with blister formation
• DIF: Perilesional skin biopsy demonstrating IgG/complement deposition on epithelial keratinocyte cell surfaces

For patients with isolated oral disease:

• Histology: Perilesional oral mucosa biopsy (sensitivity 71% for DIF in oral biopsies vs. 61% in normal skin) 1
• DIF: Uninvolved buccal mucosa (preferred site) (sensitivity 89% in oral biopsies) 1
• Technique: Evert cheek, place thumb at commissure, reflect corner of mouth with external pressure on cheek

Transport Medium for DIF Specimens

Saline for up to 24 hours is optimal and superior to liquid nitrogen 1. Michel's medium is preferred for longer transportation times (>24 hours).

Serological Testing

Indirect Immunofluorescence (IIF):

• Less sensitive than DIF but useful when biopsy is difficult (children, uncooperative adults)
• Use both mucosal and skin substrates for enhanced sensitivity:
  • Mucosal substrates better for desmoglein 3 antibodies
  • Skin substrates better for desmoglein 1 antibodies
• Limitation: Cannot be relied upon for disease monitoring due to imperfect correlation with disease activity 1

ELISA Testing:

• Direct measurement of desmoglein 1 and desmoglein 3 antibodies
• Higher sensitivity than IIF
• DIF and ELISA should be considered complementary 1
• Requires 5 mL of blood for both IIF and ELISA
• Emerging evidence: Salivary desmoglein 3 IgG detectable by ELISA (61% sensitivity in saliva vs. 74% in serum) 1

Pre-Treatment Investigations

Before initiating therapy, obtain:

• Complete blood count with differential
• Renal function (urea, electrolytes)
• Liver function tests
• Fasting glucose and HbA1c
• Fasting lipids
• Antinuclear antibody (to differentiate pemphigus erythematosus)
• Urinalysis
• Blood pressure, weight, height (in children)
• Pregnancy test in women of childbearing age
• Bone density scan (for osteoporosis prevention with corticosteroid use)
• Baseline disease activity score and quality of life assessment 1

Common Diagnostic Pitfalls

• Delayed diagnosis in oral-only disease: High index of suspicion needed for persistent oral erosions
• Inadequate biopsy technique: Must take perilesional (not lesional) tissue for histology
• Wrong DIF site: In oral disease, take DIF from uninvolved buccal mucosa, not from lesional tissue
• Relying solely on IIF: Less sensitive than DIF; use as adjunct only
• Transport delays: Saline transport optimal only up to 24 hours; use Michel's medium for longer periods