It is estimated that 35 million people worldwide had dementia in 2010, but by 2050 that number will exceed 115 million. Today, most people have relatives or know someone who is suffering from dementia. But what is dementia, exactly?
The word “dementia” has become synonymous with Alzheimer’s disease (AD) - almost as if the latter were the proper name of the former. But while AD is the most common type of dementia, it is not the only one. Different factors are combined to make the distinct dementia types, but in practice the lines between them are often unclear.
Many people automatically link memory loss with dementia, but the two shouldn’t be confused. Memory difficulties in older people can be caused by many things, such as low mood, vitamin deficiency, low thyroid function, sleep apnoea - or just being unwell.
Dementia is actually an umbrella term for a syndrome that includes memory loss, mood changes and problems with understanding, communication and reasoning. It is acquired, progressive (in contrast with damage caused by a head injury), chronic and impairs a number of cognitive processes, not just memory alone.
Ageing is the greatest risk factor for the development of dementia. While the prevalence is relatively low between ages 65 and 74, there is an exponential rise thereafter. For all dementias, the risk factors are genetic, vascular or related to lifestyle. High blood pressure, raised cholesterol levels, diabetes and smoking are typical vascular risk factors. Lifestyle variables include diet, physical activity, education, and alcohol and other toxic exposures.
As the different forms of dementia may have similar symptoms arising from different processes, the precise type can be difficult to diagnose:
- Alzheimer’s disease (AD) stems from a combination of risk factors and develops with a gradual and progressive pattern. The brain changes that contribute to the development of the symptoms are the accumulation of an abnormal protein (beta-amyloid) in plaques outside of the brain cells and a second abnormal protein (tau) that tangles within the cells.
- Vascular dementia is the second most common type after AD and is the result of multiple tiny strokes, often symptomless, that cause oxygen deprivation in many areas of brain tissue. Vascular dementia classically develops in a step-wise pattern as tissue damage progresses. Mainly the changes affect memory, but symptoms of stroke, seizures and periods of acute confusion are also common.
- Mixed dementia occurs when more than one type of dementia exists simultaneously. For example, the abnormal protein deposits of AD co-exist with blood vessel problems linked to vascular dementia. In autopsy studies, up to 50% of brains that met the pathological criteria for AD were found to have evidence of one or more coexisting dementia.
- Dementia with Lewy Bodies (DLB) shares the symptoms of Parkinson’s disease and AD. The Lewy bodies are tiny protein deposits formed in nerve cells that are linked to low levels of acetylcholine and degeneration of brain tissue.
- Fronto-temporal dementia (FTD) occurs when nerve cells in the lobes at the front and the side of the brain die and the pathways that connect them change. FTD is more common amongst those whose dementia starts before the age of 60.
Diagnosing dementia is time-consuming and can be expensive. It involves combining a medical assessment and cognitive tests with careful history-taking. A full medical examination and blood testing is needed to rule out or identify any underlying illness. Talking with family members and seeking clues of changes in patient health over time is integral. Serial neuroimaging with computerized tomography (CT) and/or magnetic resonance imaging (MRI) may reveal developing physical changes in the brain.
As to treatment, drug therapy cannot cure AD but it can slow the effects. No new treatments have become available to treat AD, or any other form of dementia, for more than a decade. Yet, significant strides have been made to pull together disparate research activities across Europe, with the hope that significant benefits will soon be translatable from the laboratory to routine clinical practice.
The brain changes from AD are believed to begin many years before the onset of clinical symptoms, so identifying biomarkers in at-risk people would be a major first step to developing significant disease altering treatments.
The importance of research into dementia cannot be overstated. While dementia does have a lower prevalence in developing countries, global patterns of morbidity and mortality are likely to converge - meaning increased burden on poorer countries.
Read my article in Risk Matters for more information about dementia.