A 38-year-old man presented to our centre with subacute cognitive decline and right limb weakness. His memory had been normal until 5 months before, initially having difficulty recalling friends’ names. Over the next 3 months, he became sleepy and lacked interest in social activities. Gradually his right limbs became inflexible, interfering with tooth brushing and walking.
An MR scan of brain at another hospital showed asymmetric confluent white matter hyperintensities, mild temporal lobe atrophy and normal intracranial arteries (figure 1). He had been treated elsewhere with intravenous immunoglobulins and corticosteroids for presumed antibody-negative autoimmune encephalitis, but his symptoms had continued to worsen despite regular immunotherapy, such that he could no longer talk or walk.
He had been previously well and was immunocompetent. There was no history of substance abuse or toxin exposure and no relevant family history.
On examination, he was alert with mixed aphasia. Cognitive assessment identified impaired…