Dementia is a group of syndromes, mostly caused by neurodegenerative diseases (such as Alzheimer’s disease, frontotemporal dementia, Lewy body dementia, corticobasal ganglion degeneration), specific pathogenic infections (paralytic dementia), cerebrovascular disease, etc. Drug treatment is ineffective, and although cholinesterase inhibitors, etc. can delay the progression of certain conditions, there is no cure. Unlike Hashimoto’s encephalopathy, the onset of dementia is due to abnormal immune-mediated vasculitis, and treatment can significantly improve the prognosis and even cure the disease. Hashimoto encephalopathy (HE) is a relatively rare syndrome characterized by elevated serum thyroid antibody levels, persistent or fluctuating neurological and psychiatric deficits and a good response to glucocorticoid therapy. Patients usually have an acute or subacute onset with a wide variety of symptoms, generally divided into 2 types, one with stroke-like manifestations and the other with dementia and psychiatric symptoms. The thyroid function is not necessarily abnormal, and a significant proportion of patients have normal thyroid function, but 100% of patients have increased anti-thyroid antibodies. The dementia type is characterized by hallucinations, memory loss, decreased intelligence, disorientation, inattention, and in severe cases, disorders of consciousness or even coma. All patients respond well to hormones, which can be said to have dramatic effects, such as the patient in this case who showed significant effects after 3 days of hormone application, the most pronounced at one week, and the condition continued to improve thereafter. The disease requires long-term administration with small amounts of hormone maintenance, and there is a risk of relapse after too rapid discontinuation, but reapplication of hormones is still effective.