[Autoimmune thyroid disease and brain]

Changes of the affective and cognitive function are usually associated with thyroid gland dysfunction. In autoimmune thyroid disease, these changes can be caused by thyroid dysfunction (hypo- or hyperthyroidism) or associated with the presence of antithyroid antibodies. Even a small change in thyroid hormone concentration is associated with change of cognitive function. In euthyroid older males, variation of total and free thyroxin accounts for about 10% of Wechsler adult intelligence test variance. In euthyroid females, lower cognitive function, measured by Mini Mental test, also correlates with blood thyroxin. Short-term (4 weeks) hypothyroidism induces clinically significant cognitivedysfunction, which is reversible by thyroid hormone substitution. Mild hypothyroidism (TSH less than 10) also induces reversible cognitive dysfunction. In hypothyroidism, PET scanning shows global reduction of brain blood flow and glucose metabolism. Hashimoto's encephalopathy is characterized by corticosteroid reversible encephalopathy associated with the presence of antithyroid antibodies. Encephalopathy can be manifested as multiple stroke-like episodes (vasculitis like), or as diffuse, progressive type characterized by dementia and psychiatric symptoms. In euthyroid patients with Hashimoto's thyroiditis and no evidence of neurological disease, SPECT showed brain perfusion abnormalities. Post mortem and brain biopsy findings can be normal or show perivascular lymphocytic infiltration. Recently, presence of antineuronal antibodies has been found in patients with Hashimoto's thyroiditis. Specific high reactivity against human alpha-enolase was high in patients with Hashimoto's encephalopathy, but absent in patients with other neurological disorders and healthy subjects. Specific antineural antibodies were found in another group of Hashimoto's encephalopathy patients. Furthermore, Ferracci et al, found antithyroid antibodies in the CSF of patients with Hashimoto's encephalopathy.