IgG4

Question 1

🎯 Essence

Answer 1

Systemic fibro-inflammatory disorder with tumour-like swelling, storiform fibrosis, obliterative phlebitis, and IgG4⁺ plasma-cell infiltrate.

Question 2

🧠 Pathophysiology

Answer 2

Th2/Treg cytokines (IL-4, IL-10, IL-13) cause IgG4 class-switching; T-fh + plasmablast expansion drive disease.

Question 3

🧬 IgG4 Feature

Answer 3

IgG4 undergoes Fab-arm exchange → functionally monovalent → poor complement activation.

Question 4

💢 Fibrosis Driver

Answer 4

M2 macrophages + TGF-β → fibroblast activation → storiform fibrosis.

Question 5

🧬 Genetics

Answer 5

HLA-DRB1*0405, CTLA-4 polymorphism linked to susceptibility.

Question 6

🔬 Histology Triad

Answer 6

Storiform fibrosis + Obliterative phlebitis + Dense IgG4⁺ plasma-cell infiltrate (>10/hpf, >40% ratio).

Question 7

🚫 Exclusions

Answer 7

Granulomas or necrosis exclude IgG4-RD; points to sarcoid/vasculitis/malignancy.

Question 8

🧩 Key Organs

Answer 8

Pancreas, salivary/lacrimal glands, retroperitoneum, kidneys, biliary tree, lungs, aorta, thyroid, meninges, prostate.

Question 9

🍌 Autoimmune Pancreatitis

Answer 9

Sausage-shaped pancreas, capsule-like rim, painless jaundice, steroid responsive.

Question 10

💧 Salivary/Lacrimal

Answer 10

Mikulicz disease: bilateral gland swelling, xerostomia, ANA–.

Question 11

🚿 Retroperitoneal Fibrosis

Answer 11

Encases ureters → hydronephrosis; check IgG4 levels.

Question 12

🏠 Kidney

Answer 12

Tubulointerstitial nephritis, cortical nodules, low C3/C4.

Question 13

🚧 Biliary

Answer 13

IgG4-sclerosing cholangitis: no beading (unlike PSC).

Question 14

🫀 Aortic

Answer 14

Periaortitis or infra-renal aneurysm.

Question 15

🧠 CNS/Orbit

Answer 15

Pachymeningitis or orbital pseudotumour mimicking malignancy.

Question 16

👨‍⚕️ GU

Answer 16

Prostatitis/epididymitis; tumour mimic.

Question 17

🧪 Serology

Answer 17

IgG4 >1.35 g/L (supportive); >2× ULN ≈ 2.7 g/L highly specific; 30% normal IgG4.

Question 18

🧪 Complement

Answer 18

Low C3/C4 (renal); ANA–, RF–; IgE/eosinophilia ~40%.

Question 19

🔍 PET

Answer 19

Symmetric multiorgan FDG uptake (SUV >4).

Question 20

📋 ACR/EULAR 2020

Answer 20

Typical organ + exclude mimics + score ≥20 = definite IgG4-RD.

Question 21

💊 Induction

Answer 21

Prednisolone 0.6 mg/kg/day ×2–4wk → taper 5 mg q2wk to 5–10 mg by 3 mo.

Question 22

💉 Steroid-Sparing

Answer 22

Rituximab first-line (anti-CD20) → depletes plasmablast precursors; AZA/MMF/MTX alternatives.

Question 23

📉 Maintenance

Answer 23

Low-dose pred or RTX q6–9mo; monitor IgG4 + imaging q3–6mo.

Question 24

📈 Relapse

Answer 24

≈40% within 1y off steroids; RTX maintains 80% remission at 12mo.

Question 25

⚠️ Complications

Answer 25

Irreversible fibrosis, organ failure, MALT lymphoma (rare).

Question 26

📊 Prognosis

Answer 26

Excellent with early therapy; fibrosis irreversible once established.

Question 27

🧠 Imaging

Answer 27

CT/MRI: capsule-like rim; T2-hypointense fibrosis.

Question 28

💡 Diagnostic Triad

Answer 28

Storiform + Phlebitis + IgG4⁺ cells → diagnostic clue.

Question 29

💡 Pitfall

Answer 29

Normal serum IgG4 in 30%; biopsy essential.

Question 30

💡 Differentials

Answer 30

Malignancy, sarcoid, AAV, Sjögren, PSC.

Question 31

💡 Steroid Response

Answer 31

Rapid improvement → key discriminator from malignancy.

Question 32

📚 NEJM 2020

Answer 32

RTX induced 97% remission in refractory IgG4-RD.

Question 33

📚 Lancet Rheumatol 2023

Answer 33

RTX > steroids for relapse prevention.

Question 34

📚 JAMA 2024

Answer 34

RTX now guideline-first for relapse prevention.

Question 35

🧩 Mnemonic 4Fs

Answer 35

Fibroinflammation + Fibrosis + False tumour + Fabulous steroid response.

Question 36

🧩 Mnemonic IgG4

Answer 36

4 clues: Plasma cells, Fibrosis, Phlebitis, Prednisolone response.