IgG4-Related Disease: Symptoms, Causes, Diagnosis, and Modern Treatment Options

Introduction

IgG4-related disease (IgG4-RD) is a long-term immune-mediated condition in which an abnormal immune response leads to inflammation, tissue enlargement, and progressive scarring (fibrosis) in one or more organs. The disease is driven by immune cells producing excessive amounts of immunoglobulin G4 (IgG4), a specific antibody subclass.

Although considered uncommon, IgG4-RD is being diagnosed more frequently worldwide due to better awareness and improved diagnostic methods. The condition often resembles cancer, infections, or other autoimmune disorders, making early recognition essential to avoid unnecessary surgeries and delays in treatment. When identified early, IgG4-RD usually responds well to medical therapy, significantly improving patient outcomes.

What Is IgG4-Related Disease?

IgG4-related disease is a systemic inflammatory disorder characterized by immune cell infiltration, tissue swelling, and fibrosis affecting various organs. The hallmark feature is the presence of IgG4-positive plasma cells within affected tissues, accompanied by a distinctive pattern of scarring.

The disease may involve a single organ or multiple organs simultaneously and often progresses slowly. Because it can form mass-like lesions, IgG4-RD is frequently mistaken for malignancy. Despite involving different organs, the underlying disease mechanism and pathological features remain consistent across all affected sites.

Commonly involved organs include:

• Pancreas

• Salivary and lacrimal glands

• Kidneys

• Bile ducts and liver

• Lungs

• Retroperitoneum

• Central nervous system

• Aorta and major blood vessels

Classification Criteria for IgG4-Related Disease

In 2019, the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) introduced standardized classification criteria to support research and clinical consistency.

The framework includes:

1. Entry criteria – Clinical or imaging findings suggestive of IgG4-RD

2. Exclusion criteria – Elimination of malignancy, infection, or other autoimmune diseases

3. Weighted scoring system – Based on pathology, imaging, serum IgG4 levels, and organ involvement

A cumulative score of 20 points or more supports classification as IgG4-RD. While useful for research, clinical judgment remains essential for diagnosis.

Causes and Risk Factors

What Triggers IgG4-Related Disease?

The precise cause of IgG4-RD is not fully understood. Current evidence suggests it develops due to a combination of immune dysregulation, genetic susceptibility, and environmental influences.

Role of IgG4 in Immune Dysfunction

Under normal conditions, IgG4 antibodies help limit excessive immune reactions. In IgG4-RD, this regulatory mechanism becomes disrupted, leading to abnormal immune activation, chronic inflammation, and tissue fibrosis.

Autoimmune and Genetic Factors

IgG4-RD shares characteristics with autoimmune diseases, including immune-mediated tissue damage. Certain genetic markers, particularly specific HLA gene variants, appear more frequently in affected individuals, suggesting a genetic predisposition.

Potential Environmental Triggers

Proposed triggers include:

• Chronic or recurrent infections

• Environmental allergens or occupational exposures

• Rare immune reactions following vaccinations (causal links remain unproven)

Who Is Most at Risk?

IgG4-RD most commonly affects middle-aged and older adults, with a higher prevalence in men. However, women and younger individuals can also develop the disease. Multi-organ involvement may occur, though risk factors for widespread disease are still under investigation.

Symptoms and Organ Involvement

General Symptoms

Symptoms often develop gradually and may be subtle in early stages. Common systemic features include:

• Persistent fatigue

• Unexplained weight loss

• Low-grade fever

• Painless swelling or mass-like lesions

Hallmark Features of IgG4-Related Disease

Pathologists look for a classic combination of findings on tissue biopsy:

• Dense lymphoplasmacytic inflammation

• Storiform (whorled) fibrosis

• Obliterative phlebitis (vein inflammation and blockage)

These features, along with increased IgG4-positive plasma cells, strongly support the diagnosis.

Organ-Specific Manifestations

Pancreas

• Autoimmune pancreatitis

• Abdominal pain, jaundice, digestive issues

Salivary and Lacrimal Glands

• Painless gland swelling

• Dry mouth and dry eyes

Kidneys

• Tubulointerstitial nephritis

• Reduced kidney function or flank pain

Lungs

• Pulmonary nodules or fibrosis

• Chronic cough or breathlessness

Liver and Bile Ducts

• IgG4-related sclerosing cholangitis

• Jaundice, itching, pale stools

Central Nervous System

• Pachymeningitis or pituitary involvement

• Headaches, vision problems, hormonal changes

Retroperitoneum

• Fibrosis causing ureteral obstruction

• Back pain or kidney dysfunction

Cardiovascular System

• Aortitis or periaortitis

• Chest or abdominal pain, aneurysm risk

Conditions That Mimic or Coexist with IgG4-RD

Commonly Associated Findings

• Elevated total IgG levels

• Increased eosinophils and IgE

• Enlarged lymph nodes

Important Differential Diagnoses

• Lymphoma and plasma cell disorders

• Multicentric Castleman disease

• Sarcoidosis

• Pancreatic or biliary cancers

• Graves’ orbitopathy

• Other autoimmune or inflammatory diseases

Because of these overlaps, tissue biopsy is often essential to confirm IgG4-RD and exclude malignancy.

How Is IgG4-Related Disease Diagnosed?

Blood Tests

• Elevated serum IgG4 levels (supportive but not definitive)

• Protein electrophoresis to rule out monoclonal disorders

Imaging

CT, MRI, and PET-CT scans help identify affected organs, disease extent, and optimal biopsy sites.

Tissue Biopsy (Gold Standard)

Histopathology confirms the diagnosis and excludes cancer or infection.

Organ-Specific Testing

Additional tests depend on organ involvement, such as kidney biopsy, liver function tests, or endocrine evaluations.

Treatment Options

Treatment aims to control inflammation, prevent fibrosis, and preserve organ function.

Corticosteroids

First-line therapy for active disease, often producing rapid symptom improvement. Careful tapering is necessary to reduce relapse risk.

Steroid-Sparing Immunosuppressants

Medications such as azathioprine, methotrexate, or mycophenolate help maintain remission and reduce steroid dependence.

Biologic Therapy

Rituximab, a B-cell–targeting agent, is highly effective for relapsing or steroid-resistant disease.

FDA-Approved Targeted Therapy

In April 2025, inebilizumab (Uplizna®) became the first FDA-approved treatment specifically for IgG4-RD, significantly reducing disease flares and steroid reliance.

Mechanical Interventions

Stenting or surgical decompression may be required for organ obstruction, often alongside medical therapy.

Monitoring and Long-Term Care

IgG4-RD frequently relapses, even after successful treatment. Long-term follow-up includes:

• Regular clinical assessments

• Laboratory monitoring

• Imaging when indicated

Multidisciplinary care involving rheumatologists, gastroenterologists, nephrologists, and other specialists is crucial for optimal outcomes.

Prognosis

With early diagnosis and appropriate therapy, most patients experience good long-term outcomes. Delayed treatment may lead to irreversible fibrosis and permanent organ damage. Relapse is common, but modern biologic therapies have significantly improved disease control.

Some studies suggest a slightly increased risk of malignancy, particularly early after diagnosis, reinforcing the need for careful follow-up.

Final Thoughts

IgG4-related disease is a complex but treatable immune-mediated condition. Early recognition, accurate diagnosis, and personalized treatment are key to preventing long-term complications. Advances in targeted therapies have transformed disease management, offering renewed hope for sustained remission and improved quality of life