Amnesic syndrome with bilateral mesial temporal lobe involvement in Hashimoto's encephalopathy

A 25-year-old woman presented with a subacute confusional state, headaches, unsteadiness, myoclonus, seizures, and an amnesic syndrome as a manifestat ion of Hashimoto's encephalopathy. Investigations showed biochemical hypoth yroidism, raised thyroid microsomal antibodies, and weakly positive antineu ronal antibodies. A T2-weighted MRI of the brain showed bilateral symmetric areas of increased signal in the mesial temporal lobes and hippocampi that had a low signal intensity on T1-weighted imaging. Despite clinical and ra diologic improvement after steroid and thyroid hormone replacement therapy, a severe amnesic syndrome with associated localized MRI abnormalities pers ists.