[Hashimoto's Encephalopathy and Autoantibodies]

Encephalopathy occasionally occurs in association with thyroid disorders, most of which are treatable. These encephalopathies include a neuropsychiatric disorder associated with hypothyroidism named myxedema encephalopathy. Moreover, Hashimoto's encephalopathy (HE) has been recognized as a new clinical disease based on an autoimmune mechanism associated with Hashimoto's thyroiditis, and can be successfully treated using steroids. Recently, we discovered that the serum autoantibodies against the NH₂-terminal of α-enolase (NAE) were a highly specific diagnostic biomarker for HE. We analyzed the serum anti-NAE autoantibodies and the clinical features in many cases of HE from institutions across Japan and other countries. About half the patients with HE had anti-NAE antibodies. Patient age was widely distributed with two peaks (around 20-30 years old and 60-80 years old). Most patients with HE were in euthyroid states and all patients had anti-thyroid antibodies. The common neuropsychiatric features include disturbance of consciousness, psychosis, cognitive dysfunction, involuntary movements, seizures, and ataxia. Electroencephalograph (EEG) abnormalities and decreased cerebral blood flow on brain single positron emission computed tomography are common findings, whereas abnormalities on brain magnetic resonance imaging are rare. Patients with HE present with various clinical phenotypes such as an acute encephalopathy form and chronic psychiatric form. Other clinical forms include limbic encephalitis, progressive cerebellar ataxia, and Creutzfeldt-Jakob disease (CJD)-mimic forms. The cerebellar ataxia form of HE clinically mimics spinocerebellar degeneration (SCD) and is characterized by the absence of nystagmus, absent or mild cerebellar atrophy, and lazy background activity on EEG. Taken together, clinicians should pay attention to the possibility of encephalopathy associated with thyroid disorders.