hashimoto thyroiditis

We just had our final exam in our pathology course, and someone had a good question on the following exam question:

Which of the following is an autoimmune disease in which patients commonly make anti-TSH-receptor antibodies?
A.  Hashimoto thyroiditis
B.  Silent thyroiditis
C.  DeQuervain thyroiditis
D.  Fibrosing thyroiditis
E.  Addison disease

Q. I was curious about the correct answer to this question, because the answer choices did not give me the choice I wanted. I was looking for Graves’ disease in the answer choices, but it was not a choice. I ended up choosing DeQuervain thyroiditis because I know it is caused by an immune cross-reaction with thyroid follicles.

A. Great question! The answer is Hashimoto thyroiditis. In Hashimoto thyroiditis, there is an autoimmune attack on the thyroid gland. Patients make antibodies against a bunch of thyroid things, including the TSH receptor. T cells are also involved in the destructive process. Check out the big lymphoid follicle with germinal center in the photo of Hashimoto disease above.

You’re right about Graves’ disease – it does have anti-TSH receptor antibodies. And you’re right about DeQuervain thyroiditis (also called subacute or granulomatous thyroiditis) being an immune cross-reaction. In DeQuervain thyroiditis, the immune system responds to a viral upper respiratory tract infection, but then cross-reacts with thyroid follicular epithelium. When the follicle epithelium is destroyed, colloid leaks out, and there’s a foreign body giant cell reaction. (There aren’t any anti-TSH receptor antibodies in DeQuervain.)

Back to Graves’ and Hashimoto thyroiditis. It seems weird that both diseases have anti-TSH receptor antibodies, since patients with Hashimoto are usually hypothyroid, and patients with Graves’ are usually hyperthyroid. What happens is that the antibodies in each disease act differently: in Hashimoto, they block the TSH receptor, but in Graves’, they stimulate the TSH receptor.

As for the other answers: silent (or lymphocytic ) thyroiditis is probably an autoimmune disease in most instances – but it is not characterized by anti-TSH receptor antibodies. Fibrosing (or Reidel) thyroiditis also may be an autoimmune disease, but is not characterized by anti-TSH receptor antibodies. And Addison disease is an autoimmune process in most patients, but the organ involved is the adrenal, not the thyroid.