A 23-year-old woman, who had been previously well, developed three generalised tonic-clonic seizures in 24 hours. For 5 days, she had complained of headache and fever, and her family had noted a personality change with unusual hypomanic behaviour (she cleaned the house persistently and wanted to stay out and party all night). She was admitted initially to a general medical ward, where she exhibited bizarre behaviour. She made strange noises, laughed inappropriately and performed repetitive stereotyped movements such as picking at her clothes. She had periods of agitation and at one point almost jumped out of the window. Brain imaging (CT and MRI) was normal. Cerebrospinal fluid (CSF) examination showed a raised lymphocyte count (140 lymphocytes/µL (≤5)) with normal CSF protein and glucose, and oligoclonal bands in CSF but not in serum. Blood cultures were sterile. Routine bloods and inflammatory markers, including serum C reactive protein, were normal. She was transferred to a neurology ward for further investigation. On the fifth day of her hospital admission, she appeared alert and was able to walk with support but had no verbal output and did not obey commands. She had limited visual tracking of people around her. She displayed waxy flexibility but with no abnormality in tone, power or reflexes. She continued with episodes of agitation, with reduced alertness, lip smacking and eye-uprolling, each lasting several minutes.

Headache followed by altered level of consciousness and seizures together with normal imaging and lymphocytic CSF suggests an encephalitic process. Infection, particularly viral encephalitis, would need to be considered. Bacterial meningoencephalitis, such as infection with Neisseria meningitides, Streptococcus pneumoniae, Haemophilus influenzae, Listeria moncytogenes or Mycobacterium tuberculosis, is possible though unlikely, but the normal CSF protein, normal peripheral blood count and lack of acute phase reaction were …