The features of Alzheimer’s disease vary from case to case, but three broad stages can be recognized.

Alzheimer’s disease starts with gradual, almost imperceptible, loss of brain function, usually first noticed as loss of memory. The loss of the ability to perform even simple arithmetical calculations, may be one of the first signs of Alzheimer’s disease. Initially, there is ordinary forgetfulness that can be compensated for by keeping memo pads and lists. The loss of memory, however, often causes anxiety.

Secondly, there is a gradual increase in the severity of the memory loss, particularly for recent events. Sometimes this stage includes an element of confusion and even invention (confabulation) to fill the gaps. At the same time there is progressive loss of awareness of the current time or place (disorientation), with uncertainty even in familiar areas and inability to give the date or even the year. Concentration declines with inability to find the right word (dysphasia). These difficulties cause alarm and frustration, and mood may change suddenly and unpredictably.

In the final stage there is severe disorientation and confusion. There may be hallucinations and false ideas of persecution (paranoid delusions). These are usually worst at night. The individual may become demanding, suspicious and sometimes violent. They become liable to ignore personal hygiene. Incontinence of urine and feces is common.

The main signs of Alzheimer’s disease are:

• Confusion. This may include misunderstanding who or where they are.
• A significant reduction in memory. This may include forgetting people's names or how to get home.
• Problems with speech and language. Small differences of meaning are lost, language becomes simplified, and conversation becomes repetitive and often irrelevant.
• Loss of interest in the outside world. This may mean the person gives up interests and hobbies or is indifferent to social conventions and to the opinions of others.

Some individuals with Alzheimer's disease may also experience these signs

• Marked emotional swings.
• Night-time confusion.
• Hallucinations.
• Changes in personality.
• Impaired judgment.
• Lack of inhibition.
• Obsessional, repetitive behavior.
• Difficulties recognizing familiar objects.
• Changes in eating habits.
• Some people may also neglect their own personal care and hygiene.