IgG4-Related Disease – A Problem With Immune System, Weight Loss, Swollen Lymph Nodes – Merck Manual

Immunoglobulin G4-related disease (IgG4-RD) is an uncommon immune disorder that usually affects multiple tissues and organs with tumor-like masses and/or painless enlargement

The exact cause of IgG4-RD is unknown, but it likely involves a problem with the immune system.

IgG4-Related Disease – Bone, Joint, and Muscle Disorders – Merck Manuals Consumer Version