It is mostly seen in middle-aged women. The onset of the disease is seasonal, for example, summer is its peak. Patients often have upper respiratory tract infections at the onset of the disease. The entire disease period can be divided into three stages: early stage with hyperthyroidism, middle stage with hypothyroidism, and recovery stage. (a) Early onset of the disease is usually rapid, with fever, fear of cold, chills, fatigue and loss of appetite. The most characteristic manifestation is pain and pressure in the thyroid gland, often radiating to the submandibular area, behind the ear or neck, and the pain worsens when chewing and swallowing. The lesion is enlarged, hard and painful. When the lesion is extensive, a large amount of thyroid hormones and non-hormonal iodinated proteins are temporarily released into the blood in the vesicles, thus, in addition to the general manifestations of infection, the common manifestations of hyperthyroidism may also be present. (b) In the middle stage, when the thyroid hormones in the thyroid alveoli are depleted due to the destruction of the infection, before the parenchymal cells of the thyroid gland are repaired, the concentration of serum thyroid hormones may drop to the level of hypothyroidism, which may be clinically transformed into hypothyroidism. (c) During the recovery period, the symptoms gradually improve and the goiter or nodules gradually disappear, and in many cases, small nodules remain and are slowly absorbed later. If treatment is timely, most patients can recover completely, and very few patients become permanently hypothyroid. In mild or atypical cases, the thyroid gland is only slightly enlarged, with mild pain and tenderness, no fever, and mild systemic symptoms, and may not be clinically hyper- or hypothyroid. The duration of the disease varies from a few weeks to more than half a year, usually about 2 to 3 months, so it is called subacute thyroiditis. The disease may recur after remission. Diagnosis Patients with fever and short-term enlargement of the thyroid gland with single or multiple nodules that are firm to the touch and significantly painful to the touch may be clinically diagnosed with this disease. Laboratory tests include increased blood sedimentation and normal or decreased white blood cells in the early stages. Blood T3 and T4 are increased, while blood TSH is decreased and the iodine uptake rate can be reduced to less than 5%-10%. This feature is important for the diagnosis of the disease. Blood thyroid immunoglobulin is also initially elevated, and its return to normal is later than that of thyroid hormones. Ultrasonography is a better test in diagnosing and determining its active phase. Ultrasound images often show hypodense lesions at the site of pressure pain. Cytocentesis or tissue biopsy may demonstrate the presence of megakaryocytes.