“Thyroiditis” means “inflammation of the thyroid gland” (any time you see “-itis,” think “inflammation”). There are four main types of thyroiditis: Hashimoto thyroiditis, subacute granulomatous (aka DeQuervain) thyroiditis, lymphocytic (aka silent) thyroiditis, and fibrosing (aka Riedel) thyroiditis. We’ll cover each of these in separate posts, starting today with subacute granulomatous thyroiditis.

Subacute granulomatous thyroiditis is a self-limiting inflammatory disorder of the thyroid that occurs following a viral upper respiratory tract infection (usually adenovirus or coxsackievirus). Several days after the infection begins, the patient develops severe neck pain, sometimes radiating to the ear. Some antigen in the virus stimulates production of CD8+ (cytotoxic) T cells which, for unclear reasons, begin to attack the thyroid follicles. As the follicles are damaged, colloid leaks out. The body sees this as foreign material, and it sends macrophages in to eat it up.

The microscopic picture looks like a foreign body giant cell reaction – because that is, in effect, what is happening. There are lots of macrophages, and you can see them ingesting colloid. Sometimes they form loose granulomas, and sometimes they become multinucleated (as in the multinucleated giant cell in the above photo).

The good news is that this process, though painful and scary-looking microscopically,  resolves on its own within a few weeks. Patients return to normal thyroid function, with no residual symptoms.