- Probable - simple things can't be performend
- Possible - s/sx eg dementia
- definite - confirmation via autopsy
- Acquired without trauma to brain
- kuru virus - from monkey
- psychosocial theory - loner
- too much stress
- decrease acetylcholine
- autoimmune theory (HIV, RA, lupus, cancer)
- aluminum theory - exposure
- pugilistica theory - contradicts to #1; exist also in parkinsons disease eg. boxers