Causes of dementia

Dementia is usually caused by degeneration in the cerebral cortex, the part of the brain responsible for thoughts, memories, actions, and personality. Death of brain cells in this region leads to the cognitive impairments that characterise dementia.

Some causes of dementia are treatable. These include, among others, head injury, brain tumours, infections (such as meningitis, HIV / AIDS, or syphilis), simple and normal pressure hydrocephalus (i.e. when the fluid in which the brain floats is collecting outside or in the cavities of the brain, compressing it from outside), hormone disorders (i.e. that is, disorders of hormone-secreting and hormone-regulating organs such as the thyroid gland), metabolic disorders (i.e. such as diseases of the liver, pancreas, or kidneys that disrupt the balances of chemicals in the blood), hypoxia (i.e. poor oxygenation of the blood), nutritional (i.e. vitamin) deficiencies, drug abuse, or chronic alcoholism1.

Unfortunately, most disorders associated with dementia are progressive (inducing a gradual decline of functioning), degenerative (i.e. getting steadily worse over time), and irreversible. The two major degenerative causes of dementia are Alzheimer's disease (the progressive loss of nerve cells without known cause) and vascular dementia (i.e. loss of brain function due to a series of small strokes).

Alzheimer's disease (AD)

Alzheimer's disease (AD) is the most common irreversible cause of dementia, accounting for 50% to 70% of all dementia cases2. AD is caused by abnormal deposits of protein in the brain that destroy cells in the areas of the brain that control memory and mental functions. A leading scientific hypothesis on the origins of AD indicates that the accumulation of beta amyloids is the primary underlying disease mechanism driving its progression.

Beta amyloids are proteins that create plaque-like deposits in the brain. They accumulate gradually and progressively as a result of an imbalance between production and clearance of peptides. Only when neuronal loss progresses and a certain threshold is reached do the clinical symptoms of AD start to appear. Because beta amyloid build-up happens gradually over time, it can take between 10 and 20 years before a patient begins showing any obvious signs of the disease.3.

AD prevention is not presently possible. However, there are two known risk factors for developing the disease

• Advancing age: About 5% of people above 65 years of age, about 20% of those over 80 years, and about 30% of those over 90 suffer from AD4.
• Family history: Currently, there is only one known gene that actually influences AD development, but there are more genes influencing the risk of developing AD that still remain to be found. There are likely to be new discoveries of susceptibility genes in the next few years. Statistically, people who have a parent or sibling affected by AD are two to three times more likely to develop the disease than those with no family history. If more than one close relative has been affected by the disease, the risk increases even more5.

Vascular dementia

Vascular dementia is the second most common cause of dementia, accounting for about 20% of cases6. This dementia is caused by atherosclerosis, caused by, for example, deposits of fats, dead cells, and other debris that form on the inside of arteries and partially (or completely) block blood flow. These blockages may cause multiple strokes, or interruptions of blood flow, to the brain. Because this interruption of blood flow is also called "infarction," this type of dementia is sometimes called multi-infarct dementia. Vascular dementia is often related to high blood pressure, high cholesterol, heart disease, diabetes, and related conditions7. Treating those conditions can slowdown the progress of vascular dementia, but functions are not recovered once they are lost.

Vascular dementia may occur at the same time as AD, resulting in a condition called Mixed Dementia.8.

Other

Other irreversible medical conditions that can cause dementia (at a much lower rate) include, for example, Parkinson's disease, Huntington's Disease, Pick's Disease, or Creutzfeldt-Jakob Disease9.