Hashimoto's encephalopathy (HE) is an uncommon syndrome associated with Hashimoto's thyroiditis. Originally described in 1966, it remains a somewhat controversial disorder . HE is most often characterized by a subacute onset of confusion with altered level of consciousness, seizures, and myoclonus. In contrast to the cognitive dysfunction associated with hypothyroidism or hyperthyroidism, HE is believed to be an immune-mediated disorder rather than representing the direct effect of an altered thyroid state on the central nervous system.
Although there is some debate regarding the appropriateness of the term Hashimoto's encephalopathy, it remains the most widely used term to describe this syndrome. Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) and a more general term, nonvasculitic autoimmune meningoencephalitis, are also used to describe this condition.
Hashimoto's encephalopathy will be reviewed here. Hashimoto's thyroiditis and other neurologic complications of thyroid disease are discussed separately. (See "Pathogenesis of Hashimoto's thyroiditis (chronic autoimmune thyroiditis)" and "Myxedema coma" and "Neurologic manifestations of hypothyroidism" and "Neurologic manifestations of hyperthyroidism and Graves' disease".)
The mechanism of Hashimoto's encephalopathy (HE) is unknown. It does not appear to be directly related to hypothyroidism or hyperthyroidism, as the majority of reported patients are euthyroid at the time of presentation. A toxic effect of increased thyrotropin-releasing hormone on the central nervous system has been proposed, as some patients appear to improve with thyroid supplementation despite being euthyroid [2-4]. However, these cases appear to be the exception rather than the rule.
The bulk of evidence points to an autoimmune vasculitis or other inflammatory process, perhaps associated with immune complex deposition, and possibly disrupting the cerebral microvasculature [2,5]: