[Prion disease]

Human prion diseases are classified into 3 categories according to etiologies: idiopathic of unknown cause, acquired of infectious origin, and genetic by PRNP mutation. The surveillance committee have analyzed 2,494 cases and identified 1,402 as prion diseases. Most of them are idiopathic, namely sporadic CJD (77%) with less genetic and acquired prion diseases (17% and 5%, respectively). The number of patients identified by the surveillance committee in these years is about 120 which are less than the number of annual death of prion disease. The difference might be due to partly the fact our surveillance need the consent from patients' family and is not complete. The mean age at onset of prion disease is late 60s while the range is fairly wide. Brain MRIs and increase of CSF 14-3-3 and tau protein levels are very characteristic. Classical sporadic CJD could show completely normal T1WI with patchy high signals in the cerebral cortex and basal ganglia on DWI. In Japan, classical sporadic CJD (MM1) is most popular but there are some rare atypical subtypes. Among them, MM2-thalamic CJD is hardest to diagnose because it shows no high intensity signals on DWI, in addition to frequent absence of CSF and EEG characteristics. In this case, CBF decrease in the thalamus on SPECT is very helpful. Genetic prion diseases in Japan are quite distinct from those in Europe. V180I and M232R mutations are unique to Japan and show sporadic CJD phenotype. Dura graft-associated CJD (dCJD) are composed of 67% of classical sporadic CJD phenotype and 33% of atypical phenotype showing slower progression with amyloid plaques. Trace-back experiments suggested the PrP(sc) of the atypical dCJD was likely to be modified from infection of abnormal VV2 protein. Although there are some atypical forms of prion diseases as mentioned above, almost all prion cases could be diagnosed with EEG, MRI, genetic test, CSF test and SPECT. We also have some incidents in which brain surgery was done before the diagnosis of prion disease and many other patients were operated using the same operating instruments before their sterilization against prion disease had been done. The explanation of possibility of prion disease infection to the patients and their follow-up was started by the incident committee. It is very important for all the nations to cooperate with each other in order to overcome this intractable disease.