Being treatable, steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), or Hashimoto’s encephalopathy, should be distinguished from untreatable conditions. Our patient was a previously healthy 89-year-old man, who presented with cognitive and balance deterioration over several months. His cerebrospinal fluid (CSF) examination was positive for protein 14-3-3 but no other test suggested Creutzfeldt–Jacob disease. His condition improved markedly, although not fully, with intravenous corticosteroids. In control CSF sampling, protein 14-3-3 was negative but a biomarker signature consistent with Alzheimer’s disease was observed. SREAT should be considered also in the very elderly in case of subacute encephalopathy.