American Board of Internal Medicine (ABIM) Certification Practice Exam

How is the diagnosis of IgG4-related disease primarily confirmed?

1. Imaging studies

2. Clinical symptoms alone

3. Tissue biopsy and histology

4. Autoantibody tests

The correct answer is: Tissue biopsy and histology

The confirmation of IgG4-related disease is primarily achieved through tissue biopsy and histological evaluation. In this context, obtaining a sample of affected tissue allows for a thorough examination under a microscope to identify characteristic features associated with the disease. Key histological findings that aid in diagnosis include a dense lymphoplasmacytic infiltrate, storiform fibrosis, and at least a moderate increase in IgG4-positive plasma cells compared to IgG-positive plasma cells. A significant ratio of IgG4-positive cells, often noted to be greater than 40%, supports the diagnosis. While imaging studies can help assess the extent of organ involvement and may provide diagnostic clues, they do not provide definitive confirmation of the disease. Clinical symptoms, while important in guiding the diagnostic process, are not sufficient for diagnosis on their own due to the variability and overlap with other conditions. Autoantibody tests can also be utilized, but they are not specific to this disease and cannot confirm the diagnosis of IgG4-related disease. Thus, the tissue biopsy and subsequent histological analysis remain the cornerstone for accurate diagnosis.