There are many different forms of dementia and each has its own causes. Alzheimer’s Disease is the most common form of dementia, accounting for between 50% and 70% of all dementias.
The effects of the different types of dementia are similar, but not identical, as each one tends to affect different parts of the brain.
Dementia, also referred to as senility, is a broad category of brain diseases that cause a long term and often gradual decrease in the ability to think and remember that is great enough to affect a person’s daily functioning. Other common symptoms include emotional problems, problems with language, and a decrease in motivation.
A person’s consciousness is usually not affected. A dementia diagnosis requires a change from a person’s usual mental functioning and a greater decline than one would expect due to aging. These diseases also have a significant effect on a person’s caregivers.
The most common symptoms of Alzheimer’s disease are short-term memory loss and word-finding difficulties. People with Alzheimer’s disease also have trouble with visual-spatial areas (for example, they may begin to get lost often), reasoning, judgment, and insight. Insight refers to whether or not the person realizes he/she has memory problems.
Common early symptoms of Alzheimer’s include repetition, getting lost, difficulties keeping track of bills, problems with cooking especially new or complicated meals, forgetting to take medication, and word-finding problems.
The part of the brain most affected by Alzheimer’s is the hippocampus. Other parts of the brain that show shrinking (atrophy) include the temporal and parietal lobes. Although this pattern suggests Alzheimer’s, the brain shrinkage in Alzheimer’s disease is very variable, and a scan of the brain cannot actually make the diagnosis.
Vascular dementia is the cause of at least 20% of dementia cases, making it the second most common cause of dementia. It is caused by disease or injury affecting the blood supply to the brain, typically involving a series of minor strokes.
The symptoms of this dementia depend on where in the brain the strokes have occurred and whether the vessels are large or small. Multiple injuries can cause progressive dementia over time, while a single injury located in an area critical for cognition (i.e. hippocampus, thalamus) can lead to sudden cognitive decline.
On scans of the brain, a person with vascular dementia may show evidence of multiple strokes of different sizes in various locations. People with vascular dementia tend to have risk factors for disease of the blood vessels, such as tobacco use, high blood pressure, atrial fibrillation, high cholesterol or diabetes, or other signs of vascular disease such as a previous heart attack or angina.
Dementia With Lewy Bodies
Dementia with Lewy bodies (DLB) is a dementia that has the primary symptoms of visual hallucinations and “Parkinsonism.” Parkinsonism is a term that describes a person with features of Parkinson’s disease. This includes tremor, rigid muscles, and a face without emotion.
The visual hallucinations in DLB are generally very vivid hallucinations of people and/or animals and they often occur when someone is about to fall asleep or just waking up. Other prominent symptoms include problems with attention, organization, problem solving and planning (executive function), and difficulty with visual-spatial function.
Again, imaging studies cannot necessarily make the diagnosis of DLB, but some signs are particularly common. A person with DLB often shows occipital hypoperfusion on SPECT scan or occipital hypometabolism on a PET scan. Generally, a diagnosis of DLB is straightforward and unless it is complicated, a brain scan is not always necessary.
Progressive Supranuclear Palsy
Progressive supranuclear palsy (PSP) is a form of dementia that is characterized by problems with eye movements. Generally the problems begin with difficulty moving the eyes up and/or down (vertical gaze palsy). Since difficulty moving the eyes upward can sometimes happen in normal aging, problems with downward eye movements are the key in PSP.
Other key symptoms of PSP include falls backwards, balance problems, slow movements, rigid muscles, irritability, apathy, social withdrawal, and depression. The person may also have certain “frontal lobe signs” such as perseveration, a grasp reflex and utilization behavior (the need to use an object once you see it).
People with PSP often have progressive difficulty eating and swallowing, and eventually with talking as well. Because of the rigidity and slow movements, PSP is sometimes misdiagnosed as Parkinson’s disease.
On scans of the brain, the midbrain of people with PSP is generally shrunken (atrophied), but there are no other common brain abnormalities visible on images of the person’s brain.
Mild Cognitive Impairment
Mild cognitive impairment means that the person exhibits memory or thinking difficulties, but those difficulties are not severe enough to meet criteria for a diagnosis of dementia. He or she should score between 25–30 on the MMSE.
Around 70% of people with MCI go on to develop some form of dementia. MCI is generally divided into two categories.
The first is one that is primarily memory loss (amnestic MCI). The second category is anything that is not primarily memory difficulties (non-amnestic MCI). People with primarily memory problems generally go on to develop Alzheimer’s disease. People with the other type of MCI may go on to develop other types of dementia.
Diagnosis of MCI is often difficult, as cognitive testing may be normal.
Corticobasal degeneration is a rare form of dementia that is characterized by many different types of neurological problems that get progressively worse over time. This is because the disorder affects the brain in many different places, but at different rates. One common sign is difficulty with using only one limb.
One symptom that is extremely rare in any condition other than corticobasal degeneration is the “alien limb.” The alien limb is a limb of the person that seems to have a mind of its own, it moves without control of the person’s brain.
Other common symptoms include jerky movements of one or more limbs (myoclonus), symptoms that are different in different limbs (asymmetric), difficulty with speech that is due to not being able to move the mouth muscles in a coordinated way, numbness and tingling of the limbs and neglecting one side of the person’s vision or senses. In neglect, a person ignores the opposite side of the body from the one that has the problem.
For example, a person may not feel pain on one side, or may only draw half of a picture when asked. In addition, the person’s affected limbs may be rigid or have muscle contractions causing strange repetitive movements (dystonia).
The area of the brain most often affected in corticobasal degeneration is the posterior frontal lobe and parietal lobe. Still, many other part of the brain can be affected.