“Thyroiditis is essentially thyroid inflammation,” Baker says. Thyroiditis can cause pain in the thyroid, or lead it to produce too much or too little thyroid hormone. Some may start to develop symptoms over time, after the inflammation has been impacting the thyroid for a while. The most common cause of thyroiditis is an autoimmune disease, which causes the immune system to mistakenly send antibodies to attack the thyroid gland. The specific one most frequently associated with thyroiditis (and that then causes hypothyroidism) is called Hashimoto’s disease. Hashimoto’s is more common in women, Baker says, and it tends to be inherited. Having another autoimmune disease can also increase your chances of developing Hashimoto’s.
Within the first year after childbirth, some women may develop postpartum thyroiditis that lasts anywhere from a few weeks up to a few months. The inflammation can cause a period of hyperthyroidism followed by period of hypothyroidism, or for some, just one or the other. For most women, the condition is transient, Baker explains, clearing up in a year or so. “But sometimes it can be permanent.” The exact cause isn’t clear, but according to the Mayo Clinic, it is believed that women who develop postpartum thyroiditis actually have an underlying autoimmune disorder before pregnancy that flares up after giving birth.
Having a viral or bacterial infection can also cause antibodies to attack the thyroid, similarly to Hashimoto’s. Some medications, like the heart medication amiodarone, can also cause thyroiditis.