Following this first description, HE is currently defined as a rare condition characterized by encephalopathy and central nervous system dysfunction, in the absence of detectable infection and/or structural abnormalities of the Central Nervous System (CNS), in the presence of positive tests for thyroid auto-antibodies (auto-Ab), either anti-thyreoperoxidase antibodies (TPO-Ab) or anti-thyroglobulin antibodies (Tg-Ab). This evidence concerns the gene TG and thyroiditis.