Definition of Subacute thyroiditis:

Subacute thyroiditis involves inflammation of the thyroid gland that usually follows an upper respiratory infection and then subsides.

Causes, incidence, and risk factors:

Subacute thyroiditis is an uncommon condition thought to be caused by viral infection of the thyroid gland. The condition often occurs after a viral infection of the upper respiratory tract. Mumps virus, influenza virus, and other respiratory viruses have been found to cause subacute thyroiditis.

The most prominent feature of subacute thyroiditis is gradual or sudden onset of pain in the region of the thyroid gland. Painful enlargement of the thyroid gland may persist for weeks or months. The condition is sometimes associated with fever. Hoarseness or difficulty swallowing may also develop.

Symptoms of thyroid hormone excess (hyperthyroidism) such as nervousness, rapid heart rate, and heat intolerance may be present early in the disease. Later, symptoms of too little thyroid hormone (hypothyroidism) such as fatigue, constipation, or cold intolerance may occur. Eventually, thyroid gland function returns to normal.

Subacute thyroiditis occurs most often in middle-aged women with recent symptoms of viral respiratory tract infection.