Subacute lymphocytic thyroiditis
Subacute lymphocytic thyroiditis is a form of thyroiditis. Subacute lymphocytic thyroiditis may occur at any age and is more common in females. A variant of subacute lymphocytic thyroiditis occurs postpartum: postpartum thyroiditis.  Both of these entities can be considered subtypes of Hashimotos thyroiditis and have an autoimmune basis. Anti-thyroid antibodies are common in all three and the underlying histology is similar.   This disorder should not be confused with de Quervains thyroiditis which is another form of subacute thyroiditis.

Symptoms and signs
Subacute lymphocytic thyroiditis features a small goiter without tenderness.  This condition tends to have a phase of hyperthyroidism followed by a return to a euthyroid state, and then a phase of hypothyroidism, followed again by a return to the euthyroid state. The time span of each phase can vary; however, each phase usually lasts 2–3 months.

Diagnosis
Subacute lymphocytic thyroiditis can only be diagnosed correctly by taking a radioactive iodine uptake test (RAIU) test. During both the hyperthyroid and hypothyroid phases, radioiodine uptake is decreased. This situation contrasts greatly with the elevated iodine uptake found in patients with Graves disease.

Treatment
Treatment is based on symptoms. Beta-blockers relieve rapid heart rate and excessive sweating during the hyperthyroid phase.


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