Your pathology report for IgG4-related sialadenitis

by Jason Wasserman MD PhD FRCPC
August 29, 2024

IgG4-related sialadenitis is a chronic inflammatory condition that affects the salivary glands, which produce saliva in your mouth. It is part of a group of IgG4-related diseases (IgG4-RD). In this condition, the immune system produces too much of an antibody called IgG4, leading to inflammation and swelling of the salivary glands. The inflammation can cause the glands to enlarge and, over time, may lead to scarring and reduced saliva production.

What are the symptoms of IgG4-related sialadenitis?

The symptoms of IgG4-related sialadenitis can vary depending on the severity of the condition. Common symptoms include:

  • Swelling of the salivary glands: This often affects the glands in front of the ears (parotid glands) and under the jaw (submandibular glands).
  • Dry mouth: Reduced saliva production can lead to dry mouth, which may make swallowing, speaking, or tasting food difficult.
  • Pain or discomfort in the salivary glands: Some people may experience mild pain or tenderness in the affected glands.
  • Swelling in other parts of the body: Since IgG4-related sialadenitis is part of a systemic (body-wide) disease, some patients may also have swelling in other areas, such as the pancreas, kidneys, or lymph nodes.

What causes IgG4-related sialadenitis?

The exact cause of IgG4-related sialadenitis is not well understood. It is believed to be an autoimmune condition in which the immune system mistakenly attacks the body’s own tissues. In this case, the immune system produces an excessive amount of IgG4 antibodies, which leads to chronic inflammation of the salivary glands. The reason why the immune system becomes overactive in this way is still being studied.

How is this diagnosis made?

The diagnosis of IgG4-related sialadenitis is made through a combination of clinical evaluation, imaging studies, and biopsy. Your doctor may begin by examining your symptoms and medical history. Imaging studies, such as ultrasound or MRI, can help visualize the swollen salivary glands. A biopsy, where a small sample of tissue from the affected gland is removed, is often needed to confirm the diagnosis. The tissue sample is then examined under a microscope to look for specific features of the disease.

Microscopic features of this condition

Under the microscope, IgG4-related sialadenitis typically shows several characteristic features:

  • Lymphoplasmacytic infiltrate: This refers to the presence of many lymphocytes (a type of white blood cell) and plasma cells (another type of white blood cell) within the tissue.
  • Storiform fibrosis: The inflammation can cause the tissue to become scarred, with the fibrotic tissue arranged in a pattern that looks like a woven mat (storiform pattern).
  • Obliterative phlebitis: This refers to inflammation of the veins within the affected tissue, which can lead to the veins becoming blocked or “obliterated.”
  • Increased IgG4-positive plasma cells: Immunohistochemistry (IHC) will show increased plasma cells producing IgG4 antibodies. To support a diagnosis of IgG4-related sialadenitis, there is usually an increase in the absolute number of IgG4-positive plasma cells, often more than 100 IgG4-positive cells per high-powered field (HPF). Additionally, the ratio of IgG4-positive plasma cells to total IgG-positive plasma cells should be greater than 40%. These criteria help pathologists confirm that the inflammation is related to IgG4 and distinguish it from other types of sialadenitis.

What additional tests may be performed to confirm the diagnosis of IgG4-related sialadenitis?

To confirm the diagnosis of IgG4-related sialadenitis, additional tests may be performed, including:

  • IgG4 immunohistochemistry: Immunohistochemistry (IHC) involves applying special stains to the biopsy tissue to specifically highlight IgG4-positive plasma cells. A high number of these cells in the tissue supports the diagnosis.
  • Blood tests: Blood tests can measure the levels of IgG4 in the bloodstream. Elevated IgG4 levels may be seen in patients with IgG4-related sialadenitis and other IgG4-related diseases.
  • Serum IgG4 concentration: This blood test measures the amount of IgG4 in the blood and can help support the diagnosis when levels are elevated.

These additional tests help pathologists and doctors confirm the diagnosis and rule out other conditions that may have similar symptoms or appearances under the microscope.

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