IgG4-related disease is becoming increasingly recognized as a cause for chronic inflammation with fibrosis and organ dysfunction. Multiple tissues may be involved. Shown here is a fibrous proliferation with infiltrates of plasma cells, typical of the inflammatory reaction that can involve multiple tissues.

The diagnosis of IgG4-RD can be made with the following 3 criteria:

1. Organ involvement

2. Serum IgG4 level exceeding 135 mg/dL

3. Microscopic finding of more than 10 IgG4+ plasma cells per high-power field and an IgG4:IgG-positive plasma cell ratio of at least 40%

If only organ involvement is present with only 1 of the remaining 2 criteria, then IgG4-RD may be considered as possible, but radiologic imaging features are needed, or... the patient responds within several weeks to a course of corticoteroid therapy. Just an increase in serum IgG4 is suggestive of IgG4-RD but is not specific.