What are the symptoms? Patients with Hashimoto’s encephalitis often present with a depression of brain function (meaning that function is reduced), drowsiness and sometimes coma. Two types of Hashimoto’s encephalitis have been described: the relapsing and remitting type (where symptoms at times worse and other times better) – which manifests with encephalopathy (a change in function or structure of the brain) and ‘stroke-like’ episodesthe diffuse progressive (widely dispersed) type – which has a slow onset and a progressive course with occasional fluctuations and manifests with psychiatric symptoms, such as confusion, disorientation and psychosis. Either of these may present with tremors, jerks or epileptic seizures. What are the causes? Currently, the exact cause is unknown. High levels of thyroid antibodies are a marker of Hashimoto’s encephalitis rather than the cause of the condition. Thyroid function is usually normal. How is it diagnosed? It is a diagnosis of exclusion and the differential (alternative diagnoses that are similar to the condition) is wide, ranging from stroke-like episodes, Alzheimer’s diseases, Creutzfeldt-Jakob disease, to rare inborn errors of metabolism (see entry Inherited Metabolic disease). Useful tests to detect the presence of Hashimoto’s encephalitis include magnetic resonance imaging (MRI) of the brain, electroencephalogram (EEG), examination of the cerebrospinal fluid (CSF), endocrine and metabolic screens, and viral studies. How is it treated? Most patients with Hashimoto’s encephalitis improve after treatment with high-dose steroid, such as prednisolone. However, improvement may take weeks or even months. Because of the improvement with steroids, some experts refer to the condition as ‘steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT)’. Plasma exchange and intravenous immunoglobulin (IVIG) have been used in some patients. The prognosis with treatment is generally good. Steroids are often continued for many months. Inheritance patterns and prenatal diagnosis Inheritance patternsNone. Prenatal diagnosis None. Is there support? Information and support in the UK for Hashimoto’s Encephalitis is provided by the Encephalitis Society (see entry Encephalitis).