Dementia is the loss of mental functions--most notably thinking, memory and reasoning--caused by the destruction of brain cells. This can be caused by a head injury or stroke, but Alzheimer's disease is the most common cause of dementia. There are up to 50 other known causes, most of which are very rare. The warning signs of dementia can be subtle and easy to overlook, especially in older sufferers.
Recent Memory Loss
Everyone forgets things occasionally, only to remember them later. How many of us have walked into a room only to completely forget why we walked in there to begin with? The difference with dementia sufferers is they forget more often and never remember them. They may ask a question over and over again, forgetting both the answer and the fact that they've asked the question in the first place. Watch for repeated questions or actions or difficulty remembering recent events.
Difficulty With Familiar Tasks
Daily life is busy, and sometimes even the best of us has a complete mental blank and don't remember to serve the bread we baked with the rest of the meal. Dementia sufferers might prepare a meal and forget to serve it entirely, or not remember they made it in the first place. Or they may remember a doctor's appointment and forget how to drive or where the doctor's office is.
Problems With Language
Language can be a hard beast to tame, and some words are easy to mix up, especially if they sound alike. Trying to find the best word to convey what you mean to communicate can cause everyone to occasionally pause and stutter. But people with dementia often forget the simplest of words, or substitute inappropriate and completely different words in their place, often making themselves difficult to understand.
Changes in Mood
It's perfectly normal to be sad or moody sometimes. Everyone has good and bad days, and days where they just feel "off." People with dementia may have rapid mood swings that make no sense, maybe not even to themselves. They could be happy one minute and in tears the next. Emotions can pass over them quickly, going from confused to excited to withdrawn in rapid succession, with no real provocation.
As everything else that is affected by aging, a person's personality can change as he gets older. Who doesn't know someone who's gotten calmer or crankier as they aged? The warning sign for dementia is a drastic change in personality that comes about in a relatively short period of time. If grandma had always been very quiet and reserved but recently has become loud and boisterous, it might be worth checking for other warning signs of dementia.