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IgG4-related disease

Summary

  • Systemic fibroinflammatory condition characterised by elevated serum IgG4 levels and tissue infiltration by IgG4-positive plasma cells
  • Affects multiple organs, commonly pancreas, salivary glands, and retroperitoneum
  • Imaging findings include organ enlargement, mass-like lesions, and fibrosis

Pathophysiology

  • Exact aetiology unknown, likely autoimmune in nature
  • Characterised by:
    • Lymphoplasmacytic infiltration with IgG4-positive plasma cells
    • Storiform fibrosis
    • Obliterative phlebitis
  • Elevated serum IgG4 levels (>135 mg/dL) in 60-70% of patients
  • T helper 2 (Th2) and regulatory T (Treg) cell responses play a crucial role

Demographics

  • Predominantly affects middle-aged to elderly males
  • Male to female ratio approximately 3:1
  • Peak incidence in the sixth and seventh decades of life
  • Increasing recognition worldwide, but true prevalence unknown

Diagnosis

  • Comprehensive diagnostic criteria include:
    1. Characteristic clinical features
    2. Elevated serum IgG4 levels
    3. Histopathological findings
  • Organ-specific diagnostic criteria exist for some manifestations (e.g., autoimmune pancreatitis)
  • Differential diagnosis includes malignancy, other autoimmune conditions, and infection
  • Tissue biopsy often required for definitive diagnosis

Imaging

  • Pancreas:
    • Diffuse pancreatic enlargement ("sausage-shaped pancreas")
    • Focal pancreatic mass
    • Delayed enhancement on contrast-enhanced CT/MRI
  • Biliary system:
    • Multifocal strictures of intra- and extrahepatic bile ducts
    • Thickening of bile duct walls
  • Salivary glands:
    • Bilateral symmetrical enlargement of submandibular and parotid glands
  • Retroperitoneum:
    • Periaortic soft tissue thickening ("coated aorta")
    • Hydronephrosis due to ureteral involvement
  • Lungs:
    • Solid nodules, ground-glass opacities, or interstitial thickening
  • Orbits:
    • Enlargement of lacrimal glands and extraocular muscles

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Treatment

  • First-line therapy: Glucocorticoids
    • Typical regimen: Prednisolone 0.6-1 mg/kg/day for 2-4 weeks, followed by gradual tapering
  • Steroid-sparing agents for maintenance or refractory cases:
    • Rituximab (anti-CD20 monoclonal antibody)
    • Azathioprine
    • Mycophenolate mofetil
  • Regular monitoring of disease activity:
    • Clinical symptoms
    • Serum IgG4 levels
    • Imaging studies
  • Long-term follow-up essential due to risk of relapse and potential development of malignancy