Subepidermal blister caused by an autoimmune reaction

Aetiology

• Autoimmune
• Patient typically elderly (> 60 years)

Pathophysiology

• Anti-hemidesmosome antibodies (IgG) react with an antigen of the hemidesmosomes anchoring basal cells to basement membrane - type II hypersensitivity
  • The antigens are the BP180 and BP230 components of hemidesmosomes
• Results in complement activation and tissue damage
• This causes interruption of the dermo-epidermal junction and the formation of tense, sub-epidermal blisters that are not readily deroofed

Clinical features

Symptoms

• Pruritus (itch) - may occur weeks or months before the appearance of any visible skin lesion
• Well-demarcated erythematous plaques may occur weeks to months before the blisters
• Large, tense, extremely itchy blisters on normal skin or erythematous base
  • Typically blisters will be distributed in flexural regions of trunk or proximal limbs
• The mucous membranes are spared, except for the cicatrial variant (characterised by marked scarring and predilection for the mucous membranes)

Signs

• Blisters will be Nikolsky sign negative

Investigations

• Biopsy:

  • Immunoflorescence: shows liner IgG and complement deposited around the basal membrane (of DEJ)

  

  • Histology: subepidermal blisters and inflammatory infiltrates (mainly eosinophils) within the blister