L'encéphalopathie d'Hashimoto : puzzle diagnostique et challenge thérapeutique. À propos d'un cas avec revue de la littérature

Hashimoto's encephalopathy (HE) is a rare autoimmune-mediated and corticosteroid-responsive encephalopathy associated with increased titres of antithyroid antibodies in serum and/or in cerebrospinal fluid. Its puzzling presentation may include cognitive and behavioural dysfunction, seizures, abnormal movements, and stroke-like episodes. We report a 42-year-old man who developed acute neuropsychiatric symptoms one month after a right posterior inferior cerebellar artery (PICA) infarction. At presentation, brain MRI confirmed right PICA stroke and ruled out the presence of another stroke, inflammation, or tumour. Electroencephalography showed diffuse slowing, while cerebrospinal fluid analysis was negative except for an elevated protein level. Laboratory tests revealed high levels of anti-thyroperoxidase and anti-thyroglobulin antibodies. The diagnosis of HE was confirmed after vascular pathologies, cancer, Creutzfeldt-Jakob disease and toxic, metabolic, infectious, and other autoimmune causes of encephalopathy were excluded. The patient received 1 g of methyl-prednisolone for 5 days, followed by 1 mg/kg/day oral prednisone. After a favourable initial response, his clinical condition worsened as the corticosteroids were tapered. Epileptic seizures, cognitive decline, cerebellar ataxia, and postural tremor of the arms and legs were prominent, and there was no clinical improvement after intravenous immunoglobulin 2 g/kg. High-dose intravenous steroids were reintroduced, with a dramatic clinical response. Maintenance therapy included oral corticosteroids and methotrexate. The patient remained in good condition and was discharged from hospital. One year later on follow-up, the patient was stable on oral methotrexate. This case confirms the protean symptoms of HE at presentation and highlights the challenge of long-term treatment after an initial and usually impressive response to intravenous corticosteroids. A review of the literature is also provided.