Hashimoto's encephalopathy (HE) has been recognized as a new clinical disease that is distinct from myxedema encephalopathy, based on an autoimmune mechanism associated with Hashimoto's thyroiditis, and steroid treatment was successfully administrated. Recently, we discovered the serum autoantibodies (Abs) against the NH2–terminal of α–enolase (NAE) as a highly specific diagnostic biomarker for HE. We analyzed the serum anti–NAE Abs and the clinical features in 80 cases of HE from institutions over Japan and other countries. About a half of HE patients carried anti–NAE Abs. Most of HE patients were in euthyroid states, and all patients had anti–thyroid (TG) Abs and/or anti–thyroid peroxidase (TPO) Abs. HE consists of various clinical phenotypes such as acute encephalopathy form, chronic psychiatric form and other particular clinical forms including limbic encephalitis, progressive cerebellar ataxia and Creutzfeldt–Jakob disease (CJD)–like form. Such a wide clinical spectrum in HE easily leads to mis– or under–diagnosis of the disease. The differential diagnosis varied among viral myxedema, encephalitis, non–herpetic limbic encephalitis, spinocerebellar degeneration, schizophrenia, front–temporal lobe dementia, Alzheimer's disease, CJD and other toxic/metabolic conditions. The common neuropsychiatry features are consciousness disturbance and psychosis, followed by cognitive dysfunction, involuntary movements, seizures and ataxia. Abnormalities on EEG and decreased cerebral blood flow on the brain single photon emission computed tomography (SPECT) are common findings whereas abnormalities on brain MRI are rare. Cerebellar ataxic form of HE clinically mimics spinocerebellar degeneration (SCD), and is characterized by absence of nystagmus, absent or mild cerebellar atrophy.
The serum from a HE patient with anti–NAE Abs immunologically reacted with cultured human brain vascular endothelial cells, and merged with α–enolase in the cytoplasm. In contract, a patch–clump study using a patient's CSF containing anti–NAE Abs in rat cerebellar slices demonstrated defective glutamate release, which suggests that the Abs' target is neurons in HE.
Taken together, we should provide an attention to the possibility of Hashimoto's encephalopathy, and should search for the pathogenesis.