❓What❓
- Insidious, progressive, infiltrative disease marked by fibroinflammatory, tumor-like lesions that stain ⊕ for IgG4, show “storiform fibrosis,” & has eosinophilic/atopic features
❓Epidemiology❓
- Middle age, M > F
❓Presentation❓
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❓Diagnosis❓
Path to the Problem
- IgG4-RD is the great mimicker of our generation: if you see a syndrome of eosinophilia/atopy + ___, IgG4-RD has to join the DDx (—Dr. Mark Heslin)
Diagnosis
- Compatible syndrome + consistent pathology
- If no extra-vascular tissue sites are available for sampling, empiric immunosuppression with a therapeutic response may provide an answer:
Lab findings
- ↑ IgG4 > 135 mg/dL (75-90%; > 500 mg/dL is ~90% specific for IgG4-RD)
- ↑ IgE (often > 1000 mg/dL, 60%)
- Eosinophilia (~30%)
- Polyclonal hypergammaglobulinemia (normal CRP)
Pathology
- Lymphoplasmocytic infiltrates enriched in IgG4+ plasma cells (100%)
- Storiform fibrosis (74%)
- Obliterative phlebitis (40%)
- Eosinophilic infiltration (40%)
🔬 Note: IgG4+ plasma cells are very non-specific (even in large quantities), so the ratio of IgG4+ to IgG+ plasma cells should be more than 40% regardless of the infiltrated organ examined (2012 International Consensus Criteria)
🔬 Note: granulomas, giant cells, neutrophilic infiltrates are unusual
🎭 IgG4-RD vs. (E)GPA 🎭
- Pathologically speaking, IgG4-RD & the primary ANCA-associated vasculitides (GPA, eGPA) can be tough to tease out
- Doppelganger features
- ⊕ IgG4 staining & Storiform fibrosis
- Hypertrophic pachymeningitis
- Hypophysitis
- Orbital pseudotumor, extraocular muscle involvement
- Pulmonary nodules & other pulmonary findings
- Renal masses (GN)
- Eosinophilia, ↑ IgE (EGPA)
- ⊕ pANCA
- IgG4-RD features
- Supra-glottic inflammation more likely
- GPA features
- Sub-glottic stenosis more likely
- Granulomatous inflammation
- Necrosis
- Neutrophilic inflammation
📚 References 📚
