Conditions: Subacute Thyroiditis

Subacute thyroiditis is a condition characterized by the inflammation of the thyroid gland that occurs over a timeframe of about 2-4 months. Generally, it is a self-limited and non-contagious illness that often follows an upper respiratory tract viral infection.

During the timeline of a subacute thyroiditis episode, the affected individual progresses from a hyperthyroid state to a hypothyroid state before returning back to a normal (euthyroid) state at a variable time from the onset of the process, typically within about 2-4 months.

There are two distinct types of subacute thyroiditis: subacute lymphocytic thyroiditis, which is painless, and subacute granulomatous thyroiditis, which is painful.

Subacute lymphocytic thyroiditis (painless)

Individuals affected by subacute thyroiditis may not be particularly attuned to symptoms of hyperthyroidism or hypothyroidism, especially if they last for no more than a few months. For this reason, many patients who have painless subacute lymphocytic thyroiditis may experience the entire infection without necessarily being aware of the problem. This is the reason that subacute lymphocytic thyroiditis is called silent subacute thyroiditis. This painless subacute lymphocytic thyroiditis is known to occur spontaneously, but is also known to occur within six months after birth in 4-10% of pregnancies brought to delivery. Subacute lymphocytic thyroiditis and has some similarities to chronic (long-term) lymphocytic thyroiditis (also known as Hashimoto’s thyroiditis), including laboratory blood testing being positive for antibodies against thyroid peroxidase and/or thyroglobulin.

Subacute granulomatous thyroiditis (painful)

The painful type, subacute granulomatous thyroiditis, also called DeQuervain’s thyroiditis, often comes to medical attention by virtue of the pain, followed by observation of thyroid swelling (goiter) and demonstration of the thyroid hormone abnormalities described above. Subacute granulomatous thyroiditis often occurs following a viral upper respiratory tract infection, and thus it appears that the virus accounting for the respiratory symptoms is also responsible for the subsequent thyroid infection. Blood testing for erythrocyte sedimentation rate (ESR) and C-reactive protein are both abnormal in this condition, but are normal with subacute lymphocytic thyroiditis and Graves’.

subacute thyroiditis vs graves

Management of subacute thyroiditis is generally unnecessary, other than management of pain in the subacute granulomatous (DeQuervain’s) thyroiditis variant. Practically speaking, the differentiation between painless subacute lymphocytic thyroiditis from Graves’ disease is important, but not always easy, as these diagnoses may mimic each other, and Graves’ benefits from specific therapy.

In subacute thyroiditis, an ultrasound of the thyroid typically shows decreased blood flow, as opposed to the increased blood flow seen in Graves’ disease. A radioiodine uptake scan is also a reliable differentiator between these two diagnoses: radioiodine uptake is low in subacute thyroiditis and high throughout the whole thyroid in Graves’ disease.

Long term outlook after subacute thyroiditis

Long-term, 90% of patients with painful subacute thyroiditis experience complete and spontaneous recovery and a return to normal thyroid function. However, the thyroid glands of patients with subacute thyroiditis may exhibit irregular scarring between islands of residual functioning thyroid tissue. Up to 10% of the patients who have had subacute thyroiditis may go on to become permanently hypothyroid and require ongoing thyroid hormone replacement therapy. Rates of permanent hypothyroidism after 1) subacute granulomatous thyroiditis associated with positive antibodies against thyroglobulin and in 2) subacute thyroiditis shortly after pregnancy.