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.

• pain in the front of the neck
• tenderness when gentle pressure is applied to the thyroid gland (palpation)
• fever
• weakness
• fatigue

Other symptoms may include:

• nervousness
• heat intolerance
• weight loss
• sweating
• diarrhea
• tremor
• palpitations

Laboratory tests in the early phase of disease may reveal:

• High serum thyroglobulin level
• Low radioactive iodine uptake
• Low serum thyroid stimulating hormone (TSH) level
• High serum free T4 (thyroid hormone, thyroxine) level
• High erythrocyte sedimentation rate (ESR)

Laboratory tests in the later phase of disease may show:

• High serum TSH level
• Low serum free T4

Anti-thyroid antibodies are either undetectable or present at low levels. Thyroid gland biopsy shows characteristic "giant cell" inflammation. Laboratory abnormalities return to normal as the condition resolves.

The purpose of treatment is to reduce pain and inflammation and to treat any hyperthyroidism, if present. Anti-inflammatory medications such as aspirin or ibuprofen are used to control pain in mild cases of subacute thyroiditis.

More serious cases may require temporary treatment with steroids (for example, prednisone) to control inflammation. Symptoms of hyperthyroidism are treated with a class of medications called beta-blockers (for example, propranolol, atenolol).

Spontaneous improvement is the rule, but the illness may persist for months. Long-term or severe complications do not usually occur.

• relapse of subacute thyroiditis

Call your health care provider if symptoms of this disorder occur. Also call if you have thyroiditis and symptoms do not improve with treatment.

MMR (measles, mumps, rubella) immunization (vaccine) or flu vaccine may be helpful to prevent these causes. Other causes may not be preventable.