Dementia, no matter how progressive, will ultimately elicit certain symptoms that are often considered hallmarks of this degenerative condition. The only thing that separates a rapidly progressive form of dementia from any other form would be the speed in which the symptoms worsen. That's really the only difference. However, not all people with rapidly progressive dementia will exhibit all the same symptoms. It just depends on the person.
The most frequent symptom of rapidly progressive dementia would be a loss of memory, starting with the most recent and moving back. This may also be seen as not remembering people they know.
Many people suffering from rapidly progressive dementia will generally become easily disoriented with their surroundings, especially unfamiliar places.
Often, a person with rapidly progressive dementia will have a difficult time knowing what to do in very common situations. They wouldn't necessarily be able to rationalize something or use logic to perform a task.
Actual words may begin to escape a person with rapidly progressive dementia. They may no longer know what something is called or believe something is referred to by another name.
Many times, a person with rapidly progressive dementia will begin to change in her temperament, in that she may become easily frustrated, agitated or irritated. She may begin to exhibit extreme shits in mood from one minute to the next.
Some people with rapidly progressive dementia will begin to display fairly odd behavior, as they may become fearful or suspicious, resulting in actions that wouldn't "normally" be performed.
A person suffering from rapidly progressive dementia may also stop taking care of themselves, essentially loosing the capacity to bathe or eat.