Hashimoto Encephalopathy

What is it?

Hashimoto encephalopathy (HE) is a rare syndrome associated with Hashimoto thyroiditis. It was first described in 1966. In contrast with the cognitive dysfunction associated with hypothyroidism or hyperthyroidism, HE is believed to be an immune-mediated disorder in which antibodies that may in some patients bind to thyroid instead bind to the central nervous system. HE has an estimated prevalence of 2.1 people in 100,000. However, it’s likely that there are many more people who are undiagnosed or misdiagnosed since the condition isn’t well-understood or highly recognized.

Who is affected?

HE is more common in women than in men and occurs in all age groups.


HE commonly presents with onset over weeks of seizures, spasms and jerks in the muscles, concentration and memory problems, psychosis, paranoia, speech problems, depression, anxiety, personality changes, and movement disorders. A more acute presentation with stroke-like episodes and/or prolonged seizures have also been described. These two presentations may overlap as well.

How is it tested for?

HE is diagnosed with the use of expert-derived clinical consensus criteria. Given the rarity of HE and the lack of one biologic test that can make the diagnosis, it is easy to misdiagnose. Sometimes patients are misdiagnosed as having Creutzfeldt-Jakob disease, dementia, Alzheimer’s disease, or as having had a stroke. By definition, all HE patients have elevated antithyroid antibodies (thyroid peroxidase antibodies and/or antithyroglobulin antibodies) in blood and/or cerebrospinal fluid (CSF). Thyroid hormone is usually tested for as well, but these vary from patient to patient and are often normal. EEG shows abnormalities in the majority of patients. And the MRI is often normal.

Is there a tumor associated with this disease?

A tumor is rarely seen in HE patients.


High-dose glucocorticoids are typically the first-line treatment of HE. First-line treatment may also include intravenous immunoglobulin and plasma exchange. When the first-line treatment regimen is ineffective or has a poor response, second-line treatment (including rituximab and cyclophosphamide) can be considered.


Most patients improve completely after the onset of corticosteroids treatment, but the risk of relapse may be as high as 40%.

Reviewed by

Anusha Yeshokumar, MD, Assistant Professor of Neurology and Pediatrics Icahn School of Medicine at Mount Sinai.