IgG4-related disease (IgG4-RD) is a systemic disease that is characterized by fibroinflammatory infiltration of various organs induced by plasma cells that express IgG4 (immunoglobulin G subclass 4).
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Terminology
Since 2012, IgG4-related disease has become the preferred term 9,10. However, it has been known by many other names in the past:
IgG4-related sclerosing disease
IgG4-related systemic disease
IgG4-related systemic sclerosing disease
IgG4-syndrome, IgG4-associated disease
IgG4-related multiorgan lymphoproliferative syndrome
Epidemiology
IgG4-related diseases are more common in middle-aged or elderly males.
Clinical presentation
Clinical manifestations vary by the organ involved. These organ systems may be either synchronously or sequentially involved.
Pathology
Location
The disease spectrum is broad across organ systems:
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central nervous system
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head and neck
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thoracic
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abdominopelvic
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multisystem
inflammatory pseudotumors, e.g. presenting as paravertebral masses
Microscopic appearance
Three major histopathologic characteristics of IgG4-related disease are 9:
dense lymphoplasmacytic infiltrate
at least focally storiform fibrosis
obliterative phlebitis
Two of these features are required for a confident pathologic diagnosis of IgG4-related disease, with a few organ-specific exceptions 9. Additional supporting features are non-obliterative phlebitis and eosinophilia 9.
Immunophenotype
Immunohistochemistry should demonstrate plasma cells that stain for IgG4. IgG4+ plasma cells must account for more than 40% of IgG+ plasma cells 9. The absolute density of IgG4+ plasma cells (number per high power field (hpf)) suggestive of the diagnosis varies by organ. For example, the cutoff is >10/hpf for pancreatic biopsy specimens and >100/hpf for lacrimal and salivary glands 9.
Markers
Serology is often, but not always, abnormal in IgG4-related diseases. A serum IgG4 level >135 mg/dL is supportive of the diagnosis 9.
Supportive are also circulating plasmablasts 12.
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