American Board of Internal Medicine (ABIM) Certification Practice Exam

What condition is characterized by infiltration of various organs by IgG4-positive plasma cells leading to organ fibrosis?

1. IgG4-related interstitial nephritis

2. Membranous nephropathy

3. Diabetic nephropathy

4. Acute interstitial nephritis

The correct answer is: IgG4-related interstitial nephritis

The condition characterized by the infiltration of various organs by IgG4-positive plasma cells leading to organ fibrosis is indeed IgG4-related interstitial nephritis. This condition is part of a broader spectrum known as IgG4-related disease, which can affect multiple organ systems including the pancreas, liver, salivary glands, and kidneys. In the kidneys, this infiltration leads to interstitial nephritis, where the inflammatory process results in the replacement of healthy renal tissue with fibrous tissue, ultimately impairing kidney function. IgG4-related disease is notable for its association with elevated serum levels of IgG4 and may also present with a range of symptoms depending on the organs involved. Diagnosis often involves imaging studies or histologic examination showing infiltration of IgG4-positive plasma cells. This condition typically responds well to immunosuppressive therapies, particularly corticosteroids. The other conditions mentioned do not share the same pathophysiological mechanism of IgG4 infiltration and subsequent fibrosis as seen in IgG4-related interstitial nephritis.