yes it is possible for people to have whats called in my location early onset alzeimers. but my locations statistics say it hits people in their 40's and 50's. here in my location the health department has no reported cases below the age of 40. (to find out what your own location goes by for age of early onset alzeimer's you would need to contact your nearest department of health.

symptoms of alzheimers (your word dementia) is...

a steady decline in a persons....short term.... memory (my location specifies short term because as a person declines they regress to where they believe the long term memories are happening right now... example a person with alzheimers may not remember to turn the stove off while cooking and believe they are at a cook out/ BBQ party from 20 years ago and wander outside to set up the grill like they did 20 years ago and expect to socialize with people they knew back then who are now either moved away or dead)

a steady decline in cognitive and functioning abilities...not knowing how to do their banking when they were perfectly fine banking skills in the past, being unable to understand what a person is saying to them where in the past they had no problems understanding things and how to do things on a cognitive level, being unable to dress and feed their self when in the past they were perfectly capable and did dress and feed their self....

eventually this steady decline results in 24/7 care where a care giver or a nursing facility takes care of all their basic needs right down to changing their diapers, feeding, restraining/ geriatric services so they dont wander off or hurt someone else. some locations now even have an amber alert system for those times when someone with this wanders off and gets lost due to in their minds its not 2017, its 1990 and they are supposed to be on an airplane going somewhere, they went to in the past or other such wanderings while their mind tells them its years ago not today.

alheimers also shows up in brain scans as it is a deterioration of brain cells. when someone I know has their yearly scans you can see dark spots and how those dark spots are progressing year after year as my relative's memory, cognitive and physical functioning abilities decline.

to answer your question can it be comfused with dissociation ... no dissociation does not show dead brain cells on an MRi, dissociation doesnt cause a person to lose their bathroom abilities/ needing to wear diapers, needing to have others feed and bath, or make sure a person doesnt burn the house down.

dissociaiton is about .....feelings.... vs alzheimers is a physical health problem

my suggestion is talk with your treatment providers. they will tell you whether you were referred for testing for alzheimers when they did your psychiatric evaluation last year. they will also be able to tell you what exactly what you are diagnosed with and why they diagnosed you that way.

then if you dont agree with their assessment results from last year just ask them for an updated psychiatric evaluation.