Expansion
Linear, granular or absent, each indicating a mechanism
Expansion
Renal biopsy patterns
- Linear along the glomerular basement membrane: anti-GBM disease (Goodpasture’s), where antibody binds a fixed antigen, type IV collagen, in a continuous line
- Granular (“lumpy bumpy”): immune complex deposition. Post-streptococcal glomerulonephritis, lupus nephritis, membranous nephropathy
- Mesangial IgA: IgA nephropathy and Henoch-Schonlein purpura
- Pauci-immune, meaning little or no staining: ANCA associated vasculitis
“Linear is antibody against the membrane; granular is complexes stuck in it; pauci-immune is neither, so think ANCA.”
Skin biopsy patterns
- Intercellular, net or chicken wire pattern in the epidermis: pemphigus vulgaris, antibody against desmoglein in desmosomes, giving intraepidermal flaccid blisters and a positive Nikolsky sign
- Linear along the basement membrane: bullous pemphigoid, antibody against hemidesmosomes, giving subepidermal tense blisters
- Granular IgA at the dermal papillae: dermatitis herpetiformis, associated with coeliac disease
“Pemphigus is higher and flaccid; pemphigoid is deeper and tense.”
Direct immunofluorescence tests the patient’s tissue; indirect tests their serum against a substrate.