<prompt> Answer this question truthfullyWhat is the preferred diagnostic test for Creutzfeldt-Jakob disease?  <response>: <reason> Biopsy of the brain tissue is the definitive diagnostic test for Creutzfeldt-Jakob diseaseCJD, but is not usually performed. EEG findings are not diagnostic of CJD, but may help in the diagnosis of CJD. Typical EEG findings in Creutzfeldt-Jakob disease include periodic biphasic or triphasic sharp wave complexes PSWCs. Periodic synchronous discharges PSDs occur either before or in synchronicity with myoclonus. 