Understanding the disease

Welcome to chapter 1

This chapter introduces the essential features of IgG4-RD and how it affects the body. Whether you’re a patient, caregiver, or clinician, these lessons will help you understand why the disease is often difficult to identify. By the end, you’ll have the foundation you need to continue your learning journey.

How common is IgG4-RD?

IgG4-related disease (IgG4-RD) is considered a rare condition. The exact prevalence is unknown, but estimates suggest that it affects 1-5 cases per 100,000 people. The incidence of IgG4-RD is growing quickly, a fact that likely reflects greater recognition. Between the years 2015 and 2019, for example, the annual incidence (number of new cases diagnosed) nearly doubled.

IgG4-RD is significantly rarer than cancer, diabetes, and rheumatoid arthritis, which are common chronic illnesses affecting a vast number of people globally. IgG4-RD is what is called an “orphan” disease, which is defined (in the United States) as consisting of fewer than 200,000 cases at a given time in the U.S. Other countries have similar definitions.

Keep in mind that estimates for IgG4-RD may vary depending on the population studied and the diagnostic criteria used. In addition, IgG4-RD may be underdiagnosed, as its symptoms may overlap with other conditions.