IgG4-related skin disease pathology

Introduction

IgG4-related disease is a recently described entity. It is characterized by:

• High levels of circulating IgG4 (> 135 mg / dL) in 60 to 70% of patients
• Tissue infiltration IgG4 + plasma cells
• Fibroinflammatory change in various organs such as the pancreas, saliva, lacrimaletc.
• Surprising histological similarities between organs.

Histology of IgG4-related skin disease

• Dense lymphoplasmacytic infiltrate (figures 1,2)
• Storiform fibrosis (fibrosis in a cartwheel pattern, figure 3)
• Moderate to moderate weave eosinophilia (Figure 4)

In general, the minimum diagnostic for most tissues is 30 to 50 IgG4-positive cells per high-power field. However, in some organs or tissues, eg kidney, only 10 IgG4 positive plasma cells per high power field may be sufficient.

Special stains for IgG4-related skin disease

• The CD3 stain illustrates the dense population of T lymphocytes (Figure 5)
• CD20 staining illustrates the population of plasma cells / B cells (figure 6)
• The anti IgG4 stain that looks brown shows an impressive> 250 IgG4 + B cells in the high power field (Figure 7)

Classification of IgG4-related skin disease

Yokura et al (2014) proposed a classification of IgG4-related skin disease that divides it into primary, mass-forming lesions due to direct infiltration of plasma cells, and secondary lesions due to IgG4 mediation inflammation through secondary mechanisms.

Primary injuries include:

• Cutaneous plasmacytosis
• Pseudolymphoma and angiolymphoid hyperplasia with eosinophilia
• Mikulicz disease (inflammation of the lacrimal and salivary glands).

Secondary injuries include:

• Lesions similar to psoriasis
• Unspecified maculopapular or erythematous injuries
• Hypergammaglobulinemia, purple and urticarial vasculitis.
• Ischemic digit

The proposed diagnostic criteria on histology for skin disease are as follows:

• IgG4-related primary skin disease
• Marked lymphocyte and plasmacyte infiltration, IgG4 + / IgG +> 40%
• No. of IgG4 + cells per high power field> 10.

IgG4-related secondary skin disease

• Infiltration of plasma cells with IgG4 + / IgG +> 40% and / or perivascular IgG4 statement

Differential diagnosis of IgG4-related skin disease

Differential diagnosis of immunoglobulin G4 (IgG4-RD) -related disease is extensive and depends on the specific site of involvement and clinical presentation.