There are few endocrine diseases that can be completely cured, and subacute thyroiditis (subacute thyroiditis) is one of the few endocrine diseases that can be cured. However, if the disease is not well understood, it often leads to misdiagnosis. For example, some patients do not have obvious neck pain, but only fever, or even long-term high fever, which is easily misdiagnosed as fever caused by other reasons. If the treatment is not standardized, it often causes the condition to recur, causing unnecessary pain and burden to the patient. So, what is subthyroiditis? It is an inflammation of the thyroid gland, but it is neither caused by a bacterial infection (thyroiditis caused by bacterial or fungal infection is called septic thyroiditis) nor by autoimmune inflammation (autoimmune thyroiditis includes Graves’ disease and Hashimoto’s thyroiditis), but is a metaplasia secondary to a viral infection, often preceded by a history of viral upper respiratory tract infection 2 to 3 weeks before onset. What are the clinical symptoms of subxiphoiditis? The most prominent symptom of subarachnoiditis is pain in the lower neck, nodular enlargement of the thyroid gland with significant tenderness. Patients often have systemic symptoms such as fever and weakness, as well as thyrotoxicosis manifestations such as panic, fear of heat, and hand tremors. Laboratory tests show a marked increase in inflammatory parameters such as ESR and CRP, a mild increase in thyroid hormone levels (FT3 and FT4) and a decrease in TSH levels, similar to hyperthyroidism, but with a significant decrease in thyroid iodine uptake. This phenomenon, in which thyroid hormone levels and thyroid iodine uptake change in opposite directions, is called the “separation phenomenon” and is an important feature that distinguishes subthyroiditis from other thyroid disorders. Treatment of subthyroiditis is simple after a clear diagnosis, and a few patients can even heal on their own. For milder symptoms, non-steroidal anti-inflammatory drugs (NSAIDs) such as high-dose aspirin or naproxen or fenpropathrin can be used; for severe systemic symptoms, glucocorticoids can be used, with adequate starting doses, such as prednisone 20-30 mg/day; the dose should be reduced slowly, by 5 mg/day per week, usually for 4-6 weeks, so as to reduce recurrence. After the inflammation subsides, some patients may develop temporary hypothyroidism, which generally does not require thyroxine replacement therapy and only requires close follow-up.