Alzheimer’s disease is the most common cause of dementia.
Dementia describes a clinical syndrome that is characterised by a significant deterioration in mental function that leads to impairment of normal function.
In healthcare, we measure ‘normal function’ by activities of daily living (ADLs). These are a series of routine activities that people should be able to do without assistance. They can be broadly divided into personal tasks and domestic tasks.
Dementia can be caused by several conditions, which all manifest with poor mental performance and impaired normal functioning. The clinical manifestations of dementia can reflect the underlying aetiology.
Alzheimer's disease (AD) is a progressive neurodegenerative disorder that causes significant deterioration in mental performance. This leads to impairment in normal social and occupational function.
It is the most common cause of dementia and unfortunately an incurable condition that has a variable clinical course.
Dementia is primarily a disease of older adults.
The World Health Organisation (WHO) estimates that almost 50 million people have a diagnosis of dementia worldwide. In the UK, it is estimated that > 500,000 people have a diagnosis of AD.
The prevalence of dementia increases with age. The estimated prevalence at 60-64 years is 0.9% compared to 41.1% in those aged 95 years and over.
A significant proportion of patients with dementia remain undiagnosed and up to 54% of patients with dementia require care home placement.
The exact cause of AD remains unknown.
The overarching theory involves environmental and genetic risk factors that increase the chance of developing pathological processes, which lead to dementia.
Commonly recognised risk factors
*NOTE: alleles of the cholesterol-carrying apolipoprotein E (APOE) have also been identified as a biological risk factor for AD.
The neurodegeneration in AD is hypothesised secondary to altered amyloid and tau protein metabolism.
The brain is composed of billions of neurons. The normal functioning of theses neurons is dependent on surrounding supportive structures such as microtubules and the protein tau, which stabilise these microtubules.
Pathological changes that occur in AD leads to interruption of key neuronal process including communication, metabolism and repair. This ultimately leads to neuronal cell death.
The two key pathological changes in AD are senile plaques and neurofibrillary tangles:
Both SP and NFT are characteristic of AD but no pathognomonic. They can be seen in other neurodegenerative conditions. SP is also seen in normal ageing. Therefore, it is the amount of these pathological changes and the topographic location within the brain (e.g. hippocampus and medial temporal lobes) which is characteristic of AD.
The amyloid deposition hypothesis is supported by identification of genetic mutations in the amyloid precursor gene APP leading to early-onset AD, and evidence of neuronal apoptosis on treatment of cells with beta-amyloid. However, some patients with severe AD do not have evidence of amyloid deposition on autopsy, and other patients who had no evidence of dementia have amyloid deposition. Therefore, it is not the complete story.
Several additional mechanisms are part of the pathological processes in AD. Alongside SP and NFT, these result in neuronal cell death that leads to memory failure, personality changes and problems with activities of daily living (hallmarks of dementia).
Dementia can be difficult to identify due to the insidious and non-specific symptoms.
Many clinical features are attributable to dementia. Some are characteristic of all dementias whereas others are typical of a particular type, like AD. There is usually a slow onset of symptoms and lack of insight with accommodation to cognitive or functional changes.
It is best to consider clinical features in the following domains: cognitive impairment, behavioural and psychological symptoms of dementia (BPSD), disease-specific features and activities of daily living.
A formal mental status examination should be completed using a recognised cognitive assessment tool.
There are multiple cognitive assessment tools, which are designed to test different areas of higher cortical functioning. Cognitive domains assessed include:
There are a variety of different cognitive assessment tools that range from basic screening tools, to in-depth assessments of each cognitive domain. Here we summarise some of the main tools.
NOTE: particularly in the hospital setting, dementia needs to be differentiated from delirium, which refers to an acute confusional state. Patients with dementia can develop delirium (i.e. acute on chronic confusion). This can be difficult to distinguish and usually requires further assessment after the acute episode.
It is essential to exclude all alternative causes before making a diagnosis of dementia.
Patients with suspected dementia are usually referred to a memory clinic.
At memory clinic, patients undergo a formal history and examination (including medication review), full complement of baseline investigations including bloods and neuroimaging to exclude an underlying cause, and formal cognitive assessment.
During these investigations, the specific type of dementia may become apparent. In AD, this may be reflected by the lack of other neurological symptoms, absence of major cardiovascular risk factors and predominant impairment in memory, thinking and behaviour.
There is a diagnostic criteria for dementia based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-V).
We have simplified this into three key components:
This describes cognitive deficits in one or more of the major cognitive domains, but the deficit is insufficient to interfere with independence in daily activities.
Mild cognitive impairment is an increasingly important term because it helps identify patients at risk of progression to dementia. Patients should have regular follow-up and be advised to undertake healthy brain activities (e.g. exercise, socialising).
Dementia is a clinical syndrome that reflects deterioration from an underlying cause, the most common being AD. The main differentials to exclude in a patient with features of dementia are the three ‘D’s’:
The severity of dementia can be determined based on the level of functional inability.
Severity of dementia is determined using cognitive assessment tools (e.g. MMSE/MoCA) or rating/assessment tools (e.g. clinical dementia rating - CDR). They are based on the functional limitation of the patient and can be adapted for different types of dementia.
In general, dementia can be divided into mild, moderate or severe.
Baseline investigations are essential to exclude an alternative diagnosis.
Typical baseline investigations involve a routine set of blood tests and neuroimaging.
Typically magnetic resonance imaging (MRI) but CT may be used if MRI not available or unsuitable. Important to exclude an alternative diagnosis (e.g. brain tumour) and can be used to help characterise the type of dementia (e.g. small vessel disease in VD).
The use of biomarkers and more advanced imaging (e.g. functional MRI) are being increasingly used in a research capacity to predict the likelihood of developing AD.
Pharmacological therapy can be used in patients with AD, but it is only a small part of overall management.
The management of AD, and dementia as a whole, should involve a full assessment of the biological, psychological and social needs of the patient. With significant deterioration in normal activities of daily living, patients will become dependent on others. This means help from families, organisation of carers, and with more advancing symptoms, need for care home placement.
There are multiple facets to management, which we summarise.
Medical therapy for the treatment of dementia should be initiated by a specialist in treating patients with dementia. The two main drugs are acetylcholinesterase inhibitors and N-methyl-D-aspartic acid receptor antagonists.
Pharmacological agents are primarily indicated in patients with AD. They should not be used in patients with mild cognitive impairment.
Choice of therapy depends on severity:
Acetylcholinesterase inhibitors are associated with small improvements in cognition, neuropsychiatric symptoms, and ADLs in patients with mild-to-moderate AD. However, there is conflicting evidence on there impact on long-term outcomes (e.g. need for care home, effect on critical ADLs).
Memantine has modest effects in patients with moderate-to-severe AD in terms of reducing functional decline.
There is no cure for dementia and it is considered a life-limiting condition.
It is estimated that one in three people over the age of 65 will die with dementia and the estimated median survival after diagnosis is 3-9 years (variable).
Progression of dementia has been estimated by WHO, which is based on each stage of severity. Development of delirium on a background of dementia is associated with more rapid progression.
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