Sudden onset memory loss

[cooperhl]

My 73 year old father in law had his Pfizer vaccine in March.  He immediately lost short term memory and now has started to lose long term memory.  We have taken him for a neuropsychologist eval which revealed severe dementia of unknown origin.  All neuro image testing has been normal (CT scan, PET scan) All blood work has been normal.  He now presents like an Alzheimers patient with sexual inappropriateness but neurologist said he has the symptoms of an Alzheimers/dementia patient without having the actual disease.  I have tried researching about vaccine side effects but not finding any information that could help explain what might have happened to my father in law that was completely independent prior to the vaccine and now requires 24 hour caregivers.  
1.  Any recommendations on possible further testing?
2. Have there been any reports of dementia from the vaccine? He has had testing for 9 months and his case has not been reported as of yet.
3.  Any place we could take him that is doing testing for patients that had neurological side effects after vaccine?
4. Any treatment options?
Thank you for any help offered