Introduction: Encephalopathy associated with Hashimoto's thyroiditis has been recognized for more than 30 years and is probably underestimated.
Exegesis: We report four patients with Hashimoto's thyroiditis who presented neurological or psychiatric features. There were three women and one man, with a mean age of 68 years. Neurological presentations were various: seizures, psychotic episodes, altered consciousness, hallucinations without usual aetiological diseases (infectious, metabolic, neoplasic, vascular, etc.). Neurological investigations (EEG, brain CT, magnetic resonance imaging) were unspecific. In all cases, a moderately high CSF protein level without pleocytosis was found. Patients presented slight hypothyroidism with high titers of antithyroperoxidase antibodies. Despite hormone therapy replacement, neurological features persisted. Outcome was favorable under steroid therapy.
Conclusion: Hashimoto's encephalopathy must be considered in the face of neuropsychiatric manifestations without obvious etiology. Pathogenic mechanisms are not clear but probably involve autoimmune cerebral vasculitis because of the efficacy of steroids.