Even though Alzheimer's disease Alzheimer's disease
A neurological disease that affects memory and behaviour. It is characterized by beta-amyloid plaques and neurofibrillary tangles in the brain. There is no known cause but genetics and lifestyle are thought to play a role. is mostly a disorder of memory Memory
The ability to process information that requires attention, storage, and retrieval. and thinking, it can also interfere with a person's balance Balance
The ability to sit or stand upright without falling over or slumping into a potentially dangerous position.. This becomes more common as the dementia progresses. It reflects both problems of motor and balance control (a problem called ataxia) as well as the brain's ability to integrate complex motor sequences (a problem known as apraxia Apraxia
Apraxia is defined as the inability to carry out a previously learned motor activity, despite normal function of all the component parts (muscles, nerves, joints, etc.).  For example, experiencing difficulty dressing or using a knife and fork, are often clues that apraxia is present.). People who have impaired balance fall, and falls can be catastrophic for older people, especially if they break a hip.

As impaired balance is usually a late sign Sign
In medicine a sign is what a physician finds by examining a patient. For example, a patient with the symptom of pain might have signs of a fast heart rate, a pale face, a clammy touch and tenderness. in Alzheimer's disease, if I see a person with early dementia whose balance is impaired, I wonder about diseases other than Alzheimer's as the cause of their problems. Balance problems are classically seen when structures at the back of the brain, known as the cerebellum, are involved in the disease, but impaired balance has many causes. It is seen earlier in patients who have dementia with Lewy bodies Lewy bodies
Round clumps of protein found in the brain's neurons in many people who experience a neurodegenerative disorder., dementia in relation to Parkinson's disease Parkinson's disease
A progressive, neurodegenerative disease characterized by the death of neurons in the brain. The disease has been linked to a lack of the neurotransmitter dopamine which has consequences such as tremors, speech impediments, movement difficulties, and often dementia later in the course of the disease., or Parkinson-like disorders (such as multiple system atrophy Atrophy
The shrinkage of tissue or muscle. or corticobasal degeneration Degeneration
Deterioration, usually of tissue, to a lower or less functional form.) and with some types of dementia seen in relationship to stroke Stroke

Blood supply to the brain is interrupted, usually by a blood clot. As a result, a portion of the brain can die from not receiving enough blood and oxygen.