Subacute thyroiditis, also known as granulomatous thyroiditis, giant cell thyroiditis and de Quervains thyroiditis. Etiology This disease accounts for about 5% of thyroid disorders and is most common in women aged 40-50 years. It is generally thought to be associated with viral infections, including influenza virus, coxsackievirus, adenovirus, and mumps virus, and with HLA-B35. 10-20% of patients have thyroid autoantibodies found in the subacute phase of the disease, and these antibodies disappear when the disease resolves, presumably secondary to destruction of thyroid tissue. Clinical manifestations Viral pharyngitis, mumps, measles or other viral infections are often present 1-3 weeks prior to onset. Significant pain occurs in the thyroid area and worsens with swallowing; there may be general malaise, loss of appetite, muscle pain, fever, tachycardia, and excessive sweating. Physical examination reveals mild or moderate enlargement of the thyroid gland, sometimes unilateral enlargement is evident, the thyroid gland is hard and significantly painful to touch, and a few patients have enlarged lymph nodes in the neck. Typical laboratory tests show a “separation curve” between 131 iodine uptake rate and serum T3 and T4 levels, i.e., at the beginning of the disease, 131 iodine uptake rate decreases and serum T3 and T4 levels increase; as the disease progresses, 131 iodine uptake rate increases and serum T3 and T4 levels gradually decrease. The formation of these separation curves results from the decrease in iodine uptake caused by inflammatory damage to thyroid cells and the leakage of thyroxine stored in the thyroid follicles into the blood circulation, resulting in thyrotoxicosis; along with the repair of thyroid cells, iodine uptake is restored and serum thyroxine concentration returns to normal. At the same time, the patient’s blood sedimentation increases. Diagnosis and Differential Diagnosis The diagnosis is clear when there are systemic symptoms, goiter and pain, and when laboratory tests show a “separation curve” for 131 iodine uptake and serum T3 and T4 levels. Treatment The disease is self-limiting and has a good prognosis; lighter patients only need NSAIDs, such as aspirin. Moderate and heavy patients can be given prednisone 40-60mg/d in 3 oral doses, which can significantly relieve the symptoms and gradually reduce the dose after 8-10 days and maintain for 4 weeks. A small number of patients have relapses, and prednisone treatment remains effective after relapse. Propranolol is given for manifestations of thyrotoxicosis; levothyroxine replacement may be given appropriately for transient hypothyroidism; permanent hypothyroidism occurs rarely.