General description

Hashimoto's disease is an autoimmune thyroiditis and the most common cause of hypothyroidism, characterized by diffuse thyroid enlargement, intense lymphocyte infiltration, eosinophilic changes in follicular epithelial cells, and interstitial fibrosis. Laboratory findings often show positivity for anti-thyroid microsomal antibodies (anti-TPO antibodies) and anti-thyroglobulin antibodies, with lymphocyte infiltration observed in cytology. The condition predominantly affects women after puberty.

Hashimoto's encephalopathy, a rare and debated condition associated with Hashimoto's disease, presents with subacute, fluctuating symptoms that can change rapidly. Symptoms may include confusion, seizures, altered consciousness, stroke-like episodes, myoclonus, tremors, cerebellar ataxia, bilateral pyramidal signs, hallucinations, and dementia. Although it shares clinical features with Creutzfeldt-Jacob disease (CJD), Hashimoto's encephalopathy is responsive to steroid treatment, making it an important differential diagnosis as a treatable form of dementia.

The diagnostic criteria for Hashimoto's encephalopathy generally include:

1. encephalopathy,
2. positive anti-thyroid antibodies (anti-TPO antibodies)
3. normal or nonspecific findings in cerebrospinal fluid (CSF) and MRI
4. good response to steroid therapy

However, the pathophysiology remains unclear, and anti-TPO antibodies themselves are not directly pathogenic. Since anti-TPO antibodies are also present in healthy individuals, their presence alone is not definitive for Hashimoto's encephalopathy. Furthermore, no specific biomarker exists for this condition, as previous candidates like anti-NAE antibodies were found to lack specificity.

With recent advances identifying various autoantibodies in autoimmune encephalitis, it is possible that cases previously diagnosed as Hashimoto's encephalopathy were actually other autoimmune encephalitis. Given the ongoing debate over the disease concept, it is crucial not to hastily diagnose Hashimoto's encephalopathy based solely on positive anti-thyroid antibodies and CNS symptoms. Thorough exclusion of other diseases, particularly autoimmune encephalitis, is essential.

Radiographic features

MRI shows diffuse bilateral white matter hyperintensity on T2WI and FLAIR, without diffusion restriction or contrast enhancement. Hashimoto's encephalopathy may also present with a limbic encephalitis pattern, characterized by symmetric hyperintensity on T2WI and FLAIR with swelling in the bilateral hippocampus, amygdala, claustrum, and cingulate gyrus. Additionally, MRI may reveal DWI and T2WI/FLAIR hyperintensity in the cerebral cortex, bilateral thalamus, and basal ganglia, resembling findings seen in Creutzfeldt-Jacob disease (CJD).