IgG4-related disease (IgG4-RD) is an immune-mediated condition that can involve nearly any organ in the body. It causes inflammation and symptoms that can mimic other illnesses, which can delay a clear diagnosis and timely, effective treatment.

The condition can cause swelling, lumps, or scarring in different organs, which is why it can resemble infections, cancers, or other autoimmune diseases. This overlap often makes diagnosis challenging. Experts believe IgG4-RD stems from an overactive immune response involving specific immune cells and antibodies. With timely recognition and treatment, many people do well on steroids or targeted therapies that calm the immune system and protect affected tissues.