The thyroid gland is infected with the thyroid follicle and follicular epithelium, and at this time it is infected with viruses, such as influenza virus, mumps virus, and coxsackievirus, and viral antibodies are present in the thyroid tissue, resulting in fever. The patient has obvious pain at night, when the thyroid gland is enlarged and hardens, and the body activates endogenous pyrogens, such as the inflammatory factors leukotrienes, bradykinin, and prostacyclin, which cause pain and fever in the body, making the fever at night unusually sensitive in subarachnoiditis.