Some symptoms of dementia in the elderly are language or communication impairments, changes in mood, a loss of interest in hobbies and activities, and difficulty completing simple tasks. Further, confusion, a deteriorating sense of direction and repetitiveness are also symptoms.
Dementia in itself is not actually a disease, but rather a conglomeration of symptoms. While the leading cause of dementia is Alzheimer's disease, it can also be caused by brain damage from a stroke or injury or by other diseases. One tell-tale symptom of dementia is trouble with memory; this change is usually subtle and involve short-term memory. The elderly person might be able to remember events of years past, but they struggle with recalling where they left something, for example.
In terms of communication issues, if the elderly person is having trouble finding the right words to complete his or her sentences, this may also be a sign of dementia. When looking at mood changes, a depressed state is often an early sign of dementia. The elderly person's personality might begin to change as well, as their judgement can be affected in the early stages. Another classic symptom of dementia is difficulty in following story-lines, whether it be real-life or on TV.