Subacute thyroiditis involves swelling (inflammation) of the thyroid gland that usually follows an upper respiratory infection.

Subacute thyroiditis is a rare condition. It is thought to be caused by a viral infection. The condition often occurs after a viral infection of the upper respiratory tract, such as mumps and influenza.

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

The most obvious symptom of subacute thyroiditis is pain in the neck. Sometimes the pain can spread (radiate) to the jaw or ears. Painful enlargement of the thyroid gland may last for weeks or months.

Other symptoms include:

• Difficulty swallowing
• Fatigue
• Fever
• Hoarseness
• Tenderness when gentle pressure is applied to the thyroid gland (palpation)
• Weakness

Symptoms of too much thyroid hormone (hyperthyroidism) may include:

• Diarrhea
• Heat intolerance
• Nervousness
• Palpitations
• Sweating
• Tremor
• Weight loss

Later, symptoms of too little thyroid hormone (hypothyroidism) may occur, including:

• Cold intolerance
• Constipation
• Fatigue

Usually thyroid gland function returns to normal. But in some cases hypothyroidism may be permanent.

Laboratory tests early in the course of the disease may show:

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

Laboratory tests later in the disease may show:

• High serum TSH level
• Low serum free T4

There may be low levels of antithyroid antibodies. Thyroid gland biopsy is usually not needed, but will show a type of inflammation characteristic of this condition. Lab tests should return to normal as the condition goes away.

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

More serious cases may need 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). Antithyroid drugs or thionamides are not effective in treating this condition.

The condition should improve on its own. However, the illness may last for months. Long-term or severe complications do not usually occur.

• Permanent hypothyroidism
• Subacute thyroiditis returns after treatment

Call your health care provider if:

• You have symptoms of this disorder
• You have thyroiditis and symptoms do not improve with treatment

MMR (measles, mumps, rubella) immunization (vaccine) or flu vaccine may help prevent these conditions, which can cause subacute thyroiditis. Other causes may not be preventable.

Ladenson P, Kim M. Thyroid. In: Goldman L and Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007:chap 244.