IgG4-related skin disease.

Area of Science:

• Immunology
• Dermatology
• Pathology

Background:

• Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory condition characterized by IgG4-positive plasma cell infiltration.
• While IgG4-RD commonly affects organs like the pancreas and salivary glands, its cutaneous manifestations have been less understood.
• Skin lesions in IgG4-RD may arise from direct IgG4-positive plasma cell infiltration or secondary IgG4-mediated inflammation.

Purpose of the Study:

• To characterize and categorize the diverse spectrum of skin lesions associated with IgG4-related disease.
• To differentiate between primary IgG4-positive plasma cell-infiltrating lesions and secondary manifestations.
• To establish a classification system for IgG4-related skin disease.

Main Methods:

• Review of documented cases and presentation of novel case series.
• Histopathological analysis of skin biopsies to identify IgG4-positive plasma cell infiltration.
• Clinical correlation to categorize lesions based on morphology and proposed pathogenesis.

Main Results:

• Seven distinct subtypes of IgG4-related skin lesions were identified: cutaneous plasmacytosis, pseudolymphoma/angiolymphoid hyperplasia, Mikulicz disease, psoriasis-like eruption, unspecified maculopapular/erythematous eruptions, hypergammaglobulinaemic purpura/urticarial vasculitis, and ischaemic digit.
• Subtypes 1-3 (cutaneous plasmacytosis, pseudolymphoma, Mikulicz disease) are attributed to direct IgG4-positive plasma cell infiltration.
• Subtypes 4-7 (psoriasis-like, maculopapular, purpura/vasculitis, ischaemic digit) are considered secondary to IgG4-mediated inflammation or plasma cell activity.

Conclusions:

• IgG4-related skin disease encompasses a heterogeneous group of lesions with distinct underlying mechanisms.
• Classification into direct infiltration (types 1-3) and secondary mechanisms (types 4-7) aids in understanding pathogenesis.
• Recognition of these subtypes is crucial for accurate diagnosis and management of IgG4-RD.