What is subacute thyroiditis?
Subacute thyroiditis is a disease in which fever and thyroid pain accompanies inflammation of the thyroid gland. “Subacute” symptoms last longer than “acute” symptoms, but are not chronic. The incidence of subacute thyroiditis is approximately 12 times higher in women than in men, and it commonly occurs in females in their 30s and 40s.
The cause of subacute thyroiditis has not been identified. It often occurs after cold-like symptoms, leading researchers to believe that viruses may be involved in its development. However, no definitive conclusion has been reached.
The symptoms of subacute thyroiditis are temporary. They appear when inflammation is severe and resolve spontaneously afterwards.
- (1) Symptoms due to inflammation:
- ・Pain in the thyroid gland Pain ranges from mild pain when swallowing or touching the thyroid area to severe pain that spreads to the ears and chest even when the patient remains still.
- ・SwellingThe entire thyroid or only a portion (the left or right side) swells and hardens. The locations of swelling and pain tend to move with time, such as from the left to the right region of the gland.
- ・FeverFever may range from low to high. However, some patients may have no obvious fever.
- (2) Symptoms caused by abnormal thyroid hormones levels:
- Inflammation of the thyroid leads to the destruction of follicular cells that produce thyroid hormones. This causes hormones stored in the thyroid gland to be released into the bloodstream. As hormone levels in the blood increase, symptoms appear that are similar to those found in Basedow’s disease, such as heart palpitations and shortness of breath. After a phase of high thyroid hormone levels passes, hormone levels drop once and then gradually return to normal. When hormone levels are low, patients have few symptoms.
The following examinations are used for diagnosis.
- (1) Blood tests:
- A raised level of C-reactive protein (CRP) is an indicator of inflammation.
- Since thyroid cells are destroyed, thyroid hormone and thyroglobulin levels in the bloodstream are high.
- (2) Ultrasonography:
- Swelling and inflammatory changes of the thyroid can be observed.
- (3) Radioiodine uptake test:
- This tests is performed in order to distinguish subacute thyroiditis from other diseases with high thyroid hormone levels.
Subacute thyroiditis resolves spontaneously. However, if symptoms are severe, they may require treatment. Medications are given to treat severe pain, high fever, or if elevated hormone levels cause tachycardia.
- ・Fever and painCorticosteroids or non-steroidal anti-inflammatory drugs are selected depending on the severity of the fever or pain. The dosage of corticosteroids is usually reduced gradually according to the symptoms over 2-3 months. Patients should not suddenly discontinue medications at their own discretion.
- ・TachycardiaHigh thyroid hormone levels may cause tachycardia. In this case, medication to reduce the arrhythmia may be coadministered.
In most patients, symptoms disappear and thyroid hormone levels return to normal in 2-3 months. In some patients, however, thyroid function remains low, necessitating thyroid hormone replacement therapy. Recurrence is rare, but may occur after a decade has passed or even later.