RÉSUMÉ
Hashimoto's encephalopathy is a rare complication of autoimmune thyroiditis not associated with thyroidal function decline. We report a 50-year-old man presenting with lower motor neuron symptoms evolving over 3 years and changes in behavior associated with attentive and cognitive impairment occurring in the last few months. Memory deficits, emotional instability, marked dysarthria, mild symmetric weakness of the lower extremities and fasciculations were the most striking clinical features. EEG was diffusely slow, cranial MRI revealed multiple subcortical white matter lesions, CSF protein was slightly elevated, electromyographic recordings showed acute and chronic denervation and extremely high TPO antibody titers were found in the serum. Hashimoto's encephalopathy and lower motor neuron disease were diagnosed. As repeated high-dose intravenous methylprednisolone administration followed by oral tapering improved both central nervous system and lower motor neuron symptoms, the question was raised whether there was a common autoimmune pathogenesis of both clinically distinct diseases.