IgG4 Related Disease

Slide 1 · IgG4-Related Disease

Mechanisms, morphology and clinicopathologic patterns

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Recognize

Identify the characteristic tissue pattern.

Explain

Separate immune observations from uncertain causation.

Apply

Interpret common organ presentations and mimics.

Slide 3 · Opening diagnostic problem

An older adult has a firm pancreatic mass and a fibrosing lesion at another site.

One tissue sample contains abundant lymphocytes and plasma cells.

Question: How could a single systemic process explain both lesions?

Slide 4 · A systemic fibroinflammatory disease

IgG4-related disease links lymphoplasmacytic inflammation, fibrosis and characteristic venous involvement across organs.

It is a disease spectrum rather than a single organ diagnosis.

Slide 5 · Four recurring diagnostic observations

Cells

Lymphocytes and numerous IgG4-producing plasma cells

Stroma

Prominent fibrosis; Often storiform

Vessels

Obliterative phlebitis

Serum

IgG4 usually increased, not invariably

Slide 6 · The name does not establish the cause

Observed

IgG4-producing plasma cells are prominent in lesions.

Serum IgG4 is usually increased.

Not established

IgG4 antibodies directly cause tissue fibrosis.

A causative autoantigen has been identified.

Slide 7 · Organ involvement is widely distributed

Glandular

Salivary glands

Lacrimal/periorbital tissues

Thyroid

Pancreas

Abdominal

Biliary tree

Retroperitoneal tissues

Kidneys

Prostate

Other systems

Lungs and lymph nodes

Aorta and pericardium

Meninges

Breast and skin

Slide 8 · Disease labels that joined one spectrum

Mikulicz syndrome

Some salivary gland cases

Riedel thyroiditis

A fibrosing thyroid lesion

Retroperitoneal fibrosis

Some previously idiopathic cases

Autoimmune pancreatitis

Type 1 form

Sclerosing cholangitis

Some fibroinflammatory biliary lesions

Slide 9 · Demographic pattern

IgG4-RD most often affects middle-aged or older individuals.

A male predominance is.

Age and sex support clinical suspicion; Neither establishes a diagnosis.

Slide 10 · A common mechanism, distinct organ effects

Fibroinflammatory lesion

Distortion of local architecture

Site-specific dysfunction

A tissue response may be shared while the clinical consequence depends on anatomical location.

Slide 11 · The fundamental tissue pattern

Inflammation

Lymphoplasmacytic inflammation

Fibrosis

Storiform fibrosis

Vascular injury

Obliterative phlebitis

The three findings describe different tissue compartments of one fibroinflammatory process.

Slide 12 · Lymphocytes are a major infiltrating population

The source emphasizes lymphocytes, particularly T cells, in affected tissues.

Lymphoid inflammation accompanies plasma cells and the fibrotic reaction.

Presence of T cells does not by itself reveal the initiating antigen.

Slide 13 · Plasma cells give the lesion its name

Schematic: Dense cellular infiltrate (not a specimen)

Lymphocytes and plasma cells

IgG4 staining identifies a plasma-cell subset

Cells alone do not prove causal antibody activity

Slide 14 · Storiform fibrosis: A pattern of organization

Schematic: Interweaving collagen whorls + inflammatory cells

Whorled collagen

Nearby lymphocytes and plasma cells

Interpret alongside vascular findings

Slide 15 · Why storiform is more informative than “fibrosis”

Generic description

An organ contains increased collagen or scar-like tissue.

Does not specify its arrangement.

Pattern-level description

Collagen is arranged in a characteristic swirling/storiform pattern.

Can be considered alongside cells and venous lesions.

Slide 16 · Obliterative phlebitis: Vein involvement

Schematic: Fibrosing venous inflammation and reduced lumen

Vein with inflammatory wall

Fibrosis and inflammatory cells

Lumen markedly narrowed

Slide 17 · The triad provides a structured reading order

Identify cellular infiltrate

Examine collagen arrangement

Evaluate venous structures

Interpret in organ context

Educational review sequence—not a published diagnostic scoring system.

Slide 18 · Interpret the biopsy as a whole

IgG4-positive cells, fibrosis and venous change represent different elements of the process.

One isolated feature provides less contextual information than the combined tissue pattern.

Organ-specific architecture and competing diagnoses must remain in view.

Slide 19 · The figures show four evidence types

Bile duct gross

A sclerotic, gray-white cross section

Bile duct tissue

Storiform fibrosis

Submandibular tissue

Lymphoplasmacytic infiltrate with whorled fibrosis

Lacrimal IgG4 stain

Numerous IgG4-producing plasma cells

Slide 20 · IgG4 immunostain: What is visualized

Schematic: Dense cellular infiltrate (not a specimen)

Lymphocytes and plasma cells

IgG4 staining identifies a plasma-cell subset

Cells alone do not prove causal antibody activity

Slide 21 · Morphology first; Immunophenotype in context

Evaluate architectural injury

Recognize lymphoplasmacytic infiltrate

Assess relevant IgG4 immunostaining

Correlate with clinical distribution

Reasoning aid, not a formal case definition or sensitivity/specificity claim.

Slide 22 · The central pathogenic uncertainty

The source states that the pathogenesis of IgG4-RD is not understood.

Autoimmune mechanisms are suspected, but causative autoantigens have not been identified.

Slide 23 · IgG4 has unusual effector characteristics

Complement

IgG4 does not activate complement efficiently.

Fc receptors

IgG4 does not bind leukocyte Fc receptors.

Fibrosis

How IgG4 might induce fibrosis is unknown.

Slide 24 · Antibody abundance is not causal evidence

Association

IgG4 is abundant in lesions and often elevated in serum.

A reliable tissue association can be diagnostically valuable.

Causation

The antibody must be demonstrated to drive the lesion.

Robbins does not establish this mechanism.

Slide 25 · B cells have a supported functional role

B cells are present in immune pathways

Anti–B-cell therapy produces clinical benefit

B-cell involvement is supported

The treatment response supports biological relevance but does not specify every step of causation.

Slide 26 · B-cell antigen presentation remains a proposal

B cell

T cell

Tissue lesion

Possible antigen presentation

Inflammation / fibrosis

Proposed model; Causal links remain incompletely resolved.

Slide 27 · Autoimmunity: Suspected, not fully identified

Supported interpretation

An autoimmune process is suspected.

B-cell depletion can improve disease.

Missing evidence

No causative autoantigen is identified.

IgG4 itself is not proven to induce fibrosis.

Slide 28 · Separate three evidence levels

Observation

IgG4-rich infiltrates, fibrosis, phlebitis

Clinical intervention

Benefit from anti–B-cell antibodies

Hypothesis

Autoantigen-driven B–T-cell interactions

Slide 29 · Type 1 autoimmune pancreatitis belongs to IgG4-RD

Type 1 autoimmune pancreatitis exhibits abundant IgG4-secreting plasma cells.

It is a pancreatic manifestation of IgG4-related disease.

Robbins separates it from type 2 and checkpoint-inhibitor–related type 3.

Slide 30 · Type 1 pancreatitis has the archetypal triad

Inflammation

Storiform pancreatic fibrosis

Fibrosis

Obliterative inflammatory phlebitis

Vascular injury

Dense IgG4-rich lymphoplasmacytic inflammation

The three findings describe different tissue compartments of one fibroinflammatory process.

Slide 31 · Type 1 vs type 2 autoimmune pancreatitis

Feature

Type 1 AIP

Type 2 AIP

IgG4-rich infiltrate

Characteristic

Not abundant

Characteristic duct lesion

Not the defining feature here

Granulocytic epithelial lesion

Systemic association

IgG4-RD manifestation

Usually pancreatic; UC in a subset

Inflammation

Lymphoplasmacytic

Lymphoplasmacytic plus neutrophilic duct lesions

Slide 32 · Type 3 pancreatitis is a different setting

Trigger

Immune checkpoint inhibitor treatment

Pathology

Histology incompletely characterized

Context

Often diagnosed through imaging and enzyme abnormalities

Distinction

Should not be conflated with IgG4-related type 1 AIP

Slide 33 · Pancreatic mass: Distinguish inflammation from tumor

Presentation

Autoimmune pancreatitis can resemble carcinoma.

A pancreatic head mass is specifically noted.

Implication

Fibroinflammation cannot be assumed benign without evaluation.

Histopathology and clinical assessment matter.

Slide 34 · Therapeutic response provides a clinical clue

Autoimmune pancreatitis as steroid responsive.

Treatment response increases the clinical relevance of separating autoimmune pancreatitis from neoplasia.

Response is contextual information—not a substitute for exclusion of malignancy.

Slide 35 · IgG4-related biliary disease may appear sclerotic

The spectrum includes some forms of sclerosing cholangitis.

A grayish-white, sclerosed bile duct.

Associated histology shows a storiform fibrotic pattern.

Slide 36 · Sclerosing cholangitis: Macro-to-micro

Gray-white sclerosing bile duct

Whorled/storiform collagen

Organ-level biliary disease

Descriptive figure-to-disease linkage Fig. 6.31.

Slide 37 · Gallbladder disease can enter the spectrum

IgG4-related sclerosing cholecystitis as a rare form of chronic cholecystitis.

This extends the fibroinflammatory phenotype to the gallbladder.

It is not equivalent to labeling all chronic cholecystitis IgG4-related.

Slide 38 · Submandibular gland: Cellular and fibrotic change

Schematic: Interweaving collagen whorls + inflammatory cells

Whorled collagen

Nearby lymphocytes and plasma cells

Interpret alongside vascular findings

Slide 39 · Lacrimal gland: Immunohistochemical clue

Schematic: Dense cellular infiltrate (not a specimen)

Lymphocytes and plasma cells

IgG4 staining identifies a plasma-cell subset

Cells alone do not prove causal antibody activity

Slide 40 · Riedel thyroiditis: A fibrosing thyroid phenotype

Riedel thyroiditis is a rare thyroid disorder with extensive fibrosis.

Fibrosis can extend into contiguous neck structures.

This entity to the IgG4-RD spectrum.

Slide 41 · A hard thyroid mass can simulate carcinoma

What is observed

A hard, fixed thyroid mass with marked fibrosis.

Adjacent neck tissues may be involved.

Diagnostic risk

Clinical findings can resemble thyroid carcinoma.

The presence of fibrosis does not remove the need to evaluate malignancy.

Slide 42 · Retroperitoneal fibrosis: Systemic disease in context

Sclerosing retroperitonitis is also called idiopathic retroperitoneal fibrosis or Ormond disease.

Many cases are considered part of IgG4-related sclerosing disease.

The fibrotic tissue may extend toward mesenteric or other retroperitoneal structures.

Slide 43 · Retroperitoneal fibrosis can obstruct ureters

Fibroinflammatory tissue encases structures

Ureteral narrowing or entrapment

Hydronephrosis

Anatomical mechanism of obstructive injury.

Slide 44 · Retroperitoneal fibrosis: Microscopic clues

Storiform fibrosis can surround lymphocytes and plasma cells.

Germinal centers and eosinophils may be present.

IgG4-positive plasma cells are frequent in this setting.

Slide 45 · Not all retroperitoneal fibrosis is IgG4-RD

Category

Alternatives in Robbins

Drugs

Ergot derivatives; β-adrenergic blockers

Inflammatory disorders

Vasculitis; diverticulitis; Crohn disease

Malignancy

Lymphoma; urinary tract carcinoma

Unexplained

Some cases remain idiopathic

Slide 46 · Orbital inflammation: Assess systemic causes

Orbital fibroinflammation can involve the lacrimal gland, extraocular muscles or other compartments.

IgG4-RD should be considered before labeling such inflammation idiopathic.

Systemic involvement may coexist in retroperitoneum, mediastinum or thyroid.

Slide 47 · The orbit has important look-alikes

Inflammatory

Idiopathic orbital inflammation is lymphoplasmacytic and sometimes fibrosing.

Vasculitis or necrosis suggests other systemic inflammatory processes.

Neoplastic

Lymphomas can also occupy orbital compartments.

Tumors may resemble inflammatory masses.

Slide 48 · Other potential target organs

Thorax

Lung

Aorta

Pericardium

Excretory/reproductive

Kidney

Prostate

Other sites

Meninges

Lymph nodes

Breast

Skin

Slide 49 · Anatomy determines the presenting problem

Site

Typical structural problem supported by Robbins

Pancreas

A mass-like lesion; chronic inflammatory injury

Thyroid

A hard fixed fibrous mass

Retroperitoneum

Ureteral encasement and hydronephrosis

Orbit/lacrimal gland

Inflammatory mass or gland involvement

Biliary tract

Sclerosing lesion of bile duct

Slide 50 · Serum IgG4: Supportive, not universally elevated

Key Pathologic Findings

Serum IgG4 is usually increased.

What follows logically

“Usually” does not mean “always.”

A serum result should not be isolated from tissue and organ findings.

Slide 51 · Avoid the isolated-immunostain shortcut

IgG4-positive plasma cells identify an immunophenotype in a tissue sample.

The source also emphasizes fibrosis, phlebitis and lymphocytes.

A coherent interpretation therefore integrates morphology with organ distribution.

Slide 52 · A practical, non-criteria reasoning pathway

Recognize the organ lesion

Check architecture and inflammatory cells

Consider IgG4-RD spectrum

Evaluate alternate causes

Educational logic only—no formal diagnostic thresholds or classification criteria implied.

Slide 53 · The differential depends on the organ

Setting

Competing explanation highlighted in Robbins

Pancreatic mass

Pancreatic carcinoma; type 2 or type 3 AIP

Hard thyroid lesion

Thyroid carcinoma

Retroperitoneal mass/fibrosis

Drug injury, inflammatory disease, lymphoma, carcinoma

Orbital mass

Lymphoma and other orbital tumors

Slide 54 · Case 1: Pancreatic head mass

An older patient has a pancreatic head mass.

Tissue sections show whorled fibrosis, abundant IgG4-positive plasma cells and inflamed obliterated veins.

Question: Which AIP subtype is most consistent with this pattern?

Slide 55 · Case 1: Interpret the tissue pattern

Most consistent pattern

Type 1 autoimmune pancreatitis.

Why

Storiform fibrosis + obliterative phlebitis + IgG4-rich inflammation.

Essential caution

A pancreatic mass requires appropriate evaluation for carcinoma.

Slide 56 · Case 2: Retroperitoneal obstruction

A patient develops hydronephrosis and imaging shows fibrous tissue encasing the ureter.

Biopsy contains lymphocytes, plasma cells and storiform fibrosis.

Question: What systemic disease spectrum merits consideration?

Slide 57 · Case 2: Avoid etiologic anchoring

Working possibility

IgG4-related retroperitoneal fibrosis.

Mechanism

Fibrous encasement can obstruct the ureter.

Competing causes

Drugs, inflammatory disease and malignancy are also recognized.

Slide 58 · Case 3: Orbital fibroinflammation

A lacrimal/orbital lesion contains lymphocytes and plasma cells with fibrosis.

A separate fibrosing lesion is present in the thyroid or retroperitoneum.

Question: Why is “idiopathic orbital inflammation” an incomplete initial conclusion?

Slide 59 · Case 3: Interpret the distribution

Pattern

Orbital inflammation plus fibrosis elsewhere.

Implication

An IgG4-related systemic process should be considered.

Differential

Other inflammatory diseases and orbital lymphoma remain important.

Slide 60 · Five observations to retain

Scope

Multiorgan fibroinflammatory disorder

Cells

Lymphocytes and IgG4-rich plasma cells

Stroma

Storiform fibrosis

Vessels

Obliterative phlebitis

Causation

IgG4 pathogenicity unproven

Slide 61 · Three places to avoid overinterpretation

Serum

Usually increased ≠ always increased

Tissue stain

IgG4 positivity ≠ isolated proof of causation

Mechanism

Benefit from B-cell depletion ≠ identified autoantigen

Slide 62 · References and source scope

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Chapter 6, “IgG4-Related Disease” and Fig. 6.31.

Robbins cross-references: autoimmune pancreatitis (Chapter 19); sclerosing retroperitonitis (Chapters 16, 21); Riedel thyroiditis; biliary and orbital inflammation.

No external diagnostic classification scheme or numerical IgG4 threshold has been introduced.