Creutzfeldt Jakob disease is not as rare as once thought. You don't necessarily have to be a denizen of Papua-New Guinea and engage in cannibalism to get CJD. Any case of dementia where the deterioration has been rapid over a few months or is associated with myoclonic jerks should raise this possibility . CJD has a very characteristic appearance on EEG called periodic sharp wave complexes. In this regard it is to be noted that Hashimoto's encephalitis has been reported in the literature to closely mimic CJD with the exception that it does not cause periodic sharp wave complexes. (Seipelt et al, J Neurol Neruosurg Psychiatry , 1999 Feb, 66:2, 172-6) EEG is useful to identify an entity that can closely mimic dementia , namely pseudodementia. Most patients with pseudodementia show an intact and responsive posterior rhythm , whereas dementia patients tend to show a slowing of the posterior rhythm. Anybody who has ever seen a EEG or an EEG report is familiar with the term "slow waves". It has been found that diffuse slow wave activity in dementia mainly reflects parietal lobe dysfunction. No association appears to exist between EEG diffuse slow wave activity and frontal lobe dysfunction. ( Dementia 1995 Nov, 6:6, 323-9 ) Parietal lobe dysfunction is part of the Alzheimer dementia process. Focal abnormalties including focal slowing is more suggestive of Multi-infarct dementia than Alzheimer dementia. It has been noted in a study conducted by Gur, Neufeld et al that EEG performed after a stroke can be used as an indicator of subsequent cognitive decline. (Acta Neurol Scand 1994 Oct 90:4, 263-5)