Autoimmune, Connective Tissue and Immunobullous Diseases
Scope
The exam tests autoantibody targets, histologic cleavage levels, direct immunofluorescence patterns, and systemic associations in lupus, dermatomyositis, scleroderma, vasculitis, and immunobullous disease.
Core rules
- Lupus: interface dermatitis; DLE shows follicular plugging and scarring; SCLE is anti-Ro/SSA associated; systemic disease needs ANA, anti-dsDNA, complement.
- Dermatomyositis: Gottron papules, heliotrope, shawl sign; anti-Mi-2, anti-TIF1γ, anti-MDA5 (ulcerative, lung disease).
- Scleroderma: CREST with anti-centromere; diffuse disease with anti-Scl-70/topoisomerase I.
- Pemphigus vulgaris: anti-desmoglein 3, suprabasal acantholysis, intercellular IgG on DIF; foliaceus: anti-desmoglein 1, superficial cleavage.
- Bullous pemphigoid: anti-BP180/BP230, subepidermal blister, linear IgG/C3 at basement membrane, eosinophils.
- Dermatitis herpetiformis: granular IgA in dermal papillae; celiac disease association.
Worked example
A patient has flaccid blisters and oral erosions; histology shows a tombstone row of basal cells. Reasoning: suprabasal acantholysis with mucosal involvement indicates pemphigus vulgaris. DIF shows intercellular IgG; ELISA for anti-Dsg3 confirms. Treatment is systemic corticosteroids plus rituximab in moderate-to-severe disease.
Traps
On salt-split skin, bullous pemphigoid labels the roof; epidermolysis bullosa acquisita labels the floor. A negative DIF does not exclude pemphigus if the biopsy site is wrong. Anti-Ro can cross the placenta and cause neonatal lupus.