Immunodermatology and Connective Tissue Diseases
Core framework
Organise autoimmune bullous disease by level of split and immunofluorescence pattern. Pemphigus vulgaris: intraepidermal, suprabasal, intercellular IgG (net-like) on direct immunofluorescence, anti-desmoglein 3 (and 1). Bullous pemphigoid: subepidermal, linear IgG/C3 along basement membrane, anti-BP180/BP230, tense blisters. Dermatitis herpetiformis: granular IgA in dermal papillae, associated with coeliac disease. Epidermolysis bullosa acquisita: linear IgG on salt-split skin localising to the floor.
Connective tissue disease: lupus (interface dermatitis, photosensitivity, ANA, anti-dsDNA, anti-Sm), dermatomyositis (Gottron papules, shawl sign, anti-Mi-2, malignancy screen), systemic sclerosis (Raynaud, sclerodactyly, anti-centromere vs anti-Scl-70 vs anti-RNA polymerase III). Vasculitis: palpability implies small-vessel involvement; direct immunofluorescence helps classify (IgA in Henoch–Schönlein purpura).
Traps
- Salt-split skin: roof vs floor localisation distinguishes pemphigoid from EBA.
- Pemphigus foliaceus is superficial and lacks mucosal disease.
- Anti-centromere = limited systemic sclerosis; anti-Scl-70 = diffuse.
- Dermatomyositis in adults mandates malignancy workup.
Rule of thumb
For blistering disease, ask where is the split and what does immunofluorescence show - those two answers usually determine the diagnosis before serology.