Dementia consists of a range of progressive neurological disorders which can affect cognitive functions, such as memory, thinking, language, judgment, and comprehension.

There are several types of dementia-causing disorders, including tauopathies such as Alzheimer’s disease, Synucleinopathies such as Parkinson’s disease dementia, vascular dementia such as stroke-related dementia, and mixed dementia.

There are several causes that can lead to dementia, including the presence of degenerative neurological diseases such as Alzheimer's disease, infections, subdural hematomas, vascular disorders, chronic drug use, brain injury, and nutritional deficiencies.

Several risk factors can increase the possibility of developing the disease, such as age, Down syndrome, being female, excessive alcohol consumption, having a mild cognitive impairment, atherosclerosis, and sleep apnea.

Most types of dementia are nonreversible (degenerative). Deposition of abnormal proteins in the brain is essential to the pathology and pathogenesis of degenerative diseases that lead to dementia.

Signs and symptoms of dementia vary depending on the cause, and they may include memory loss, personality and mood changes, difficulty with coordination and motor functions, and difficulties concerning reasoning or problem-solving, in addition to the need for assisted-self-care in later stages.

To diagnose dementia, a physician may review the patient history by gathering useful information about previous cases of dementia in the family, patterns of symptoms, and medications that have been used. Furthermore, a physician may perform cognitive and neuropsychological tests such as Mini-Mental State Examination (MMSE).

Moreover, a physician may conduct a neurological evaluation and suggest brains scans such as computed tomographic (CT) scans and magnetic resonance imaging (MRI) to diagnose dementia. In addition, laboratory tests, psychiatric evaluation, and pre-symptomatic tests may be recommended in some cases.

Dementia cannot be treated, but its symptoms can be managed by medications such as cholinesterase inhibitors and memantine. Non-pharmacologic interventions may also help manage dementia; these include occupational therapy, physical therapy, and speech therapy.

If not managed appropriately, dementia can lead to many complications such as nutrient deficiencies, respiratory infections, impaired self-care, personal safety issues, and death.

There is no definitive method to prevent dementia. However, some preventive measures may help reduce the risk of developing it, including a healthy diet, healthy weight, regular exercise, and less alcohol consumption.

Dementia is a common syndrome that consists of a range of progressive neurological disorders that affect various mental and cognitive functions, such memory, thinking, language, orientation, judgment, comprehension, calculation, and learning capacity. The effects of dementia also have a profound impact on the patient’s behavior.

There are several different types of dementia depending on the cause of the condition. Some types of dementia-causing disorders include:

Tauopathies

This class of neurological disorders is caused by tau proteins in the brain in which tau prions replicate spontaneously in the frontal lobes. Tauopathies include:

• Alzheimer’s disease: This is the most common type of tauopathy and dementia. It usually affects five main areas, memory, language, cognitive ability, insight, and spatial awareness.
• Corticobasal degeneration: This progressive neurological disorder causes the gradual worsening of issues affecting memory, movement, speech, and swallowing.
• Progressive supranuclear palsy: This type of tauopathy can lead to problems concerning balance, movement, vision, speech, and swallowing.
• Argyrophilic Grain Disease: This tauopathy is relatively common, and is mainly considered a sporadic late-onset form of dementia that may lead to problems in regions of memory and emotion in the brain.
• Frontotemporal disorders (FTDs): These forms of tauopathy or dementia are relatively rare. Frontotemporal dementia leads to loss of function in certain brain regions in response to nerve cell damage.  Types of FTDs include:

1. Behavioral variant frontotemporal dementia: This FTD leads to behavioral and personality changes in affected patients.
2. Primary progressive aphasia: This is the second major type of FTD. It can lead to problems concerning speech, writing, language, and comprehension.
3. Frontotemporal dementia with parkinsonism linked to chromosome 17: FTDP-17 is an inherited, rare form of dementia that can cause behavioral and personality changes, cognitive impairment, and motor symptoms.
4. Pick’s disease: This is a rare form of dementia characterized by Pick bodies, which are abnormal collections of the tau proteins in the brain.  This disorder can cause several symptoms that resemble those of Alzheimer’s disease, such as loss of speech and inappropriate behavior.

Synucleinopathies

Synucleinopathies is a term that represents several neurodegenerative disorders that share the same feature in which cytoplasm of selective populations of neurons and glia contain fibrillary aggregates of alpha-synuclein protein. Types of synucleinopathies include:

• Dementia with Lewy bodies: This is the third most common cause of dementia after Alzheimer's disease and vascular dementia. This type can lead to distinct symptoms including difficulty sleeping, loss of smell, and visual hallucinations.
• Parkinson’s disease dementia: This type occurs in people with Parkinson’s disease who suffer from dementia with Lewy bodies. This Form of dementia can affect language, memory, social judgment, and reasoning.

Vascular Dementia

This is the second most common type of dementia, which is mainly caused by injuries to the vessels supplying blood to the brain. Some types of vascular dementia include:

• Stroke-related dementia: This form of dementia develops after a stroke. Moreover, there is a related type called multi-infarct dementia that occurs when a person has a series of small strokes that cause damage to brain cells.
• Subcortical vascular dementia: Also known as Binswanger’s disease, this form of dementia mainly results from small vessel disease that leads to changes in small blood vessels in the brain.
• Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL): This type is an inherited condition that can cause stroke and other impairments.

Mixed dementia

This form of dementia results from the simultaneous occurrence of both Alzheimer’s disease-related neurodegenerative processes and vascular disease-related processes.

Dementia is mainly caused by damage to brain cells. Several causes can lead to this damage, including:

• Degenerative neurological diseases: Alzheimer's disease and other degenerative neurological diseases, can lead to dementia.
• Infections: Infections can affect the central nervous system and alter its functions, such as syphilis, Lyme disease, and HIV, which causes AIDS dementia complex.
• Hydrocephalus: Hydrocephalus is the accumulation of cerebrospinal fluid within the brain as a result of developmental abnormalities or infections. This condition can cause permanent damage to the brain.
• Vascular problems: Vascular problems, such as stroke, can lead to dementia.
• Multiple sclerosis: A condition that affects nerve fibers in the brain and can potentially cause permanent damage, which can manifest as dementia.

Some causes of dementia are reversible and can be cured. These causes include:

• Subdural hematomas: These can lead to bleeding between the surface of the brain and the covering membrane over the brain.
• Anoxia: This condition is also called hypoxia and refers to when less oxygen is transported to the organs. This can result from breathing issues, such as asthma.
• Poisoning: This results from exposure to heavy metals, such as lead, and other poisons, such as pesticides.
• Metabolic causes: Dementia may result from changes in blood sugar, sodium, and calcium levels.
• Medications: Some medication may lead to dementia, such as some cholesterol drugs.
• Substance use: Chronic drug and alcohol abuse can result in dementia.
• Brain tumors: Brain tumors may cause dementia depending on what area of the brain they develop on.

Many factors play a role in and increase the risk of developing dementia. These risk factors include:

• Age: The risk rises as age advances, especially after age 65.
• Genetics: When a person has more than one family member with dementia, the risk of developing a genetically linked form increases.
• Down syndrome: Investigations proved that many people with Down syndrome develop early-onset Alzheimer's disease by middle age, which indicates a link between the two.
• Gender: Females are at an increased risk of developing Alzheimer's disease, but males are more at risk of developing vascular dementia than females.
• Excessive alcohol consumption: Consuming large amounts of alcohol increases the risk of dementia.  
• Mild cognitive impairment (MCI): This involves problems with memory that do not lead to loss of daily function. This condition can increase the risk of developing dementia.
• Atherosclerosis: This disease can lead to a stroke or another brain injury that results from the gradual accumulation of fats and cholesterol in blood vessels, which can hinder blood from reaching the brain.
• Head injury: Head injuries can increase the risk of developing Alzheimer's disease later in life.
• Diabetes: The risk of developing dementia increases among people with diabetes, although the evidence for this association is modest.
• Education: Poor education increases the risk of developing Alzheimer's disease, especially in males.
• Smoking: The risk of developing dementia increases among smokers because they are prone to diseases that slow or prevent blood from reaching the brain.
• Sleep apnea: The risk of developing dementia increases among people who have sleep apnea, a condition marked by snoring, because they experience frequent breathing halts while asleep.
• Hypertension: High blood pressure can lead to various complications such as stroke, cognitive decline, and types of dementia that affect the white matter in the brain.
• Stroke: The risk of developing dementia increases after stroke.
• Chemical exposure: Investigators speculate a role for chemicals such as solvents and heavy metals in developing the disease.
• Depression: Late-life depression may lead to the development of dementia, although more investigations are needed to confirm this association.
• Lipids: An independent risk factor for the development of dementia with stroke has been theorized to be elevated levels of low-density lipoproteins, also known as ‘bad’ cholesterol.
• Cerebral white matter lesions: These are more common in vascular dementia, and mostly refer to arteriosclerotic abnormalities of the small penetrating arteries and arterioles in the white matter. They can also refer to a state of demyelination, damage to and loss of the protective cover of nerve fibers, in the subcortical structures of the brain.

Most types of dementia are degenerative, or nonreversible. Alzheimer's disease is a specific neurodegenerative disease and is the most common cause of dementia in older people.

Pathologically, degenerative diseases are known to cause loss of neurons. Deposition of abnormal proteins in the brain is essential to the pathology and pathogenesis of degenerative diseases. In some degenerative diseases, normally soluble proteins misfold into a beta-pleated pattern and turn into insoluble fibrillary amyloid. However, the abnormal proteins are different in each type of dementia.

Clinically, dementia primarily represents a deterioration of function in the association cortex, which is an essential part of mental functions that are more complex than detecting basic dimensions of sensory stimulation. Moreover, abnormalities that relate to dementia are more diffuse and may extend into sensorimotor cortical areas as well.

Amyloid plaques and neurofibrillary tangles are classic neuropathological signs of Alzheimer’s disease.  Tangles consist of tau, which is a protein that normally maintains the internal structure of the nerve cell. Phosphorylation or the attachment of phosphate molecules normally modify tau. However, when levels of phosphorylation exceed the normal, the possibility of tangle formation and preventing tau from carrying out its normal functions increases.

The signs and symptoms of dementia vary depending on the cause. Common signs and symptoms include:

• Memory loss, especially problems with memory of recent events such as forgetting messages, frequently losing personal items such as a wallet, paying bills, and remembering appointments.
• Difficulties with tasks and activities that need organization and planning.
• Becoming confused in unfamiliar environments, or feeling lost in familiar ones.
• Difficulty in tracking conversations, particularly in groups.
• Personality, and mood changes, such as irritability, suspicion, fear, anxiety, and depression.
• Inappropriate behavior, such as undressing at wrong times and places.
• Difficulty finding the right word when speaking.
• Impaired judgment and difficulties concerning reasoning or problem-solving skills.
• A difficulty with numbers and/or handling money.
• Difficulty handling complex tasks.
• A difficulty with coordination, motor functions, and slower physical movements.
• Being alert, drowsy, confused, disoriented, and losing track of the time.
• Loss of appetite and weight loss.
• Difficulty tracking stories on television or in books, or trouble understanding magazine and newspaper articles.
• Loss of initiative that includes being passive and isolated.
• Changes in sleep patterns, such as waking up often at night.

Difficulty swallowing.In later dementia, symptoms may worsen and include the following:

• Difficulty recognizing close family members and friends.
• Behavioral changes may escalate and include aggression.
• Requiring assisted-self-care.
• Bladder and bowel incontinence.

A physician can often diagnose dementia using the following methods:

Patient history: The physician can gather useful information by asking questions about previous cases of dementia in the family, patterns of symptoms, and medications that have been used.

Physical exam: Measuring vital signs, especially blood pressure, is helpful in revealing conditions associated with dementia. Many of these conditions may be treatable.

Cognitive and neuropsychological tests: Many tests can be used to assess cognitive functions such as memory, orientation, reasoning, judgment, language skills, and attention. The most commonly used test to assess memory or other mental abilities is the mini-mental state examination (MMSE). This test is used primarily by clinicians to help diagnose dementia and to help assess its progression and severity.

Neurological evaluation: A physician will usually evaluate balance, sensory functions, eye movements, vision, reflexes and other functions in order to detect signs of conditions that may be treatable or which can affect the diagnosis of dementia.

Laboratory tests: Several physical problems that affect brain function can be investigated by performing simple blood tests such as complete blood count, a blood sugar test, vitamin B12 levels, and measuring sodium and other electrolytes in the blood. Other tests may include urine analysis, drug and alcohol tests, cerebrospinal fluid analysis, and an analysis of thyroid function.

Psychiatric evaluation: This assessment can help rule out other mental diseases that may cause or contribute to a person’s symptoms such as depression.

Pre-symptomatic tests: This genetic test help explore the risk of developing certain types of dementia.

Brain scans: Brain scan can help in the diagnosis of dementia in the following ways:

• CT scans and MRI: Although the use of these tests in the diagnosis of dementia remains controversial, they can help check for evidence of other conditions that may be causing dementia, such as stroke, bleeding, tumors, and hydrocephalus.
• Positron emission tomography scan: This test can reveal patterns of brain activity, in addition to deposition of amyloid proteins in the brain, which is a hallmark of Alzheimer's disease.
• Single photon-emission computed tomography: This test can measure blood flow to the brain in order to help detect patterns of altered brain activity seen in dementia patients.
• Electroencephalogram: An EEG records the brain's electrical signals, which can help detect abnormal brain activity.

Most cases of dementia cannot be cured, but its symptoms can be managed. Treatable forms of dementia usually go away when the underlying cause has been treated. Treatment for dementia includes:

Medications

Several medications can help slow down the progression of symptoms. Medications include:

• Cholinesterase inhibitors: Drugs such as donepezil, rivastigmine, and galantamine can temporarily improve or stabilize memory and thinking skills in some people with dementia.
• Memantine: An N-methyl-D-aspartate receptor antagonist, this drug can stop declines in learning and memory.
• Other medications: Physicians may prescribe other medications to manage other symptoms or conditions that accompany dementia, such as depression and sleep disturbances.

Nonpharmacologic interventions

Nonpharmacologic interventions that are useful in managing dementia include:

• Occupational therapy: The goals of this type of therapy usually focus on helping the patient take steps to manage the progression of dementia, manage behavior, and prevent accidents, such as falls.
• Physical therapy: This may include gait training or cardiovascular, flexibility, and strength exercises, in addition to a general physical fitness program to improve the patient’s balance, mobility, and overall health.
• Speech therapy: This can help in improving low voice volume and poor enunciation as well as enhancing muscular strength and treating swallowing difficulties.
• Modifying the environment: This can make it easier for patients with dementia to focus and function by reducing clutter and noise in their environment. Interventions can range from installing monitoring systems to hiding objects that can threaten safety, such as knives and car keys.

Alternative medicine: Although study results have been inconsistent in determining the effectiveness of many of the most commonly used supplements and herbs in treating dementia, some people suggest that many of these can help. These include vitamin E, B complex vitamins, zinc, melatonin, omega-3 fatty acids, phosphatidylserine.

Other alternative therapies that may help improve the quality of life of the patient, include:

• Music therapy: Mostly by listening to calming or relaxing music.
• Support groups: This can provide emotional support and practical solutions to day-to-day frustrations.
• Individual and family psychotherapy: This provides learning strategies to manage emotional and behavioral problems, and to help address concerns about the future.
• Pet therapy: This can help improve the mood of patients with dementia by the use of animals, such as visits from dogs or cats.
• Aromatherapy: This therapy uses fragrant plant oils to improve health.
• Art therapy: The use of artworks as a therapeutic technique can help patients improve their mood by focusing on the process rather than the outcome.
• Massage therapy: Massage therapy can help patients with dementia relieve stress and anxiety.

Dementia can lead to several complications that include:

• Nutrient deficiencies: Dementia can lead to reduced nutrient intake in many cases. Patients with dementia may eventually become unable to chew and swallow.
• Respiratory infections: Choking or aspirating food into the lungs can result from swallowing difficulties present in many cases of dementia, leading to respiratory infections such as pneumonia.
• Problems concerning self-care activities: Dementia can affect the patient’s ability to perform daily activities such as bathing, dressing, and using the toilet independently.
• Problems concerning personal safety: Patients with dementia are vulnerable to several safety issues that should be addressed, including driving, cooking and walking alone.
• Death: Death and coma are expected to occur in the later stages of dementia, usually because of infections.

Preventing all types of dementia is not possible, but there are some preventive measures that may help reduce the risk of developing dementia and other serious health conditions. Such measures may include:

• Healthy diet: A low-fat, high-fiber diet that include plenty of fresh fruit and vegetables and whole grains.
• Healthy weight: Being overweight or obese can increase blood pressure, which increases the risk of developing some kinds of dementia, so maintaining a healthy weight can reduce the risk.
• Regular exercise: This can help make the heart and blood circulation more efficient, reducing the risk of some types of dementia.
• Less alcohol consumption: Alcohol can elevate blood pressure, as well as raise cholesterol levels in the blood, which increases the risk of developing some kinds of dementia.
• Quit smoking: Smoking can cause narrowing of arteries, which can lead to high blood pressure.
• Avoiding head trauma: Wearing protective gear when chances of head injury or concussions are high, such as wearing a helmet when riding a bike, helps protect against injuries that may lead to dementia.

Dementia is not curable in most cases and gets worse over time, so families who have a member with the disease need to formulate a comprehensive future care plan to deal with the disease.The prognosis for most types of dementia is poor as it often has a significant effect on quality of life and lifespan.  

The WHO reports that, worldwide, around 47 million people have dementia, with 9.9 million new cases occurring every year. Alzheimer's disease is the most common cause of dementia, contributing to 60–70% of all cases.

According to data published in an article in BioMed Research International 60.1% of all people with dementia in 2001 were living in developing countries, and this is expected to increase to 71.2% by 2040.

A study published in the British Journal of Neurology, Neurosurgery and Psychiatry found that there are more than two new cases of dementia per 1000 people age 65 to 69 years, every year; furthermore, 70 new cases of dementia can be expected out of 1000 people age 90 or older, every year.

According to Alzheimer Europe, the highest prevalence rates of dementia are found in Italy, affecting around 2.09% of the population, while the lowest prevalence rates are in Slovakia and Turkey, affecting 1.07% and 0.44% of the population, respectively.