Creutzfeldt-Jacob disease mimics, or how to sort out the subacute encephalopathy patient

A 44-year-old woman was admitted under the neurology department with a 4 week history of rapid cognitive decline and mild gait unsteadiness. Her only history was of classical migraine but immediately prior to presentation she had experienced 5 weeks of persistent migrainous headache with left-sided sensory disturbance. On examination she scored 47/100 on the Addenbrooke's Cognitive Examination with deficits in all domains; she had myoclonic jerks, truncal ataxia and subtle left-sided pyramidal weakness. Initial investigation revealed normal routine bloods, normal MR brain imaging, CSF with 22x10(9)/mm(3) lymphocytes (decreasing to 6 on repeat CSF a week later), protein of 0.62 g/ l, normal glucose, red blood cell count and cytology, and positive unpaired oligoclonal bands. EEG showed bursts of frontally predominant slow wave activity. The initial concern was that she had a subacute encephalopathy, possibly sporadic CJD........