Alzheimer's Disease is a progressive neurodegenerative disease and the most common cause of dementia in the UK. It gradually damages brain cells and neural networks, producing progressive impairment in memory, thinking, language, orientation, judgement and eventually everyday functioning. The disease can begin years before symptoms become obvious, and clinical progression usually develops gradually rather than appearing suddenly.
Although increasing age is the strongest major risk factor, Alzheimer's disease is not an inevitable consequence of ageing and can occur before age 65. The NHS identifies increasing age, family history and cardiovascular-related risk factors among factors associated with increased risk. The disease is named after Alois Alzheimer, whose early twentieth-century clinical and pathological observations helped establish the characteristic relationship between cognitive decline and abnormal brain pathology.
Two major pathological features associated with Alzheimer's Disease are extracellular amyloid-beta plaques and intracellular tau neurofibrillary tangles. Amyloid-beta peptides can aggregate into plaques around neurons, while abnormal tau accumulates within neurons and disrupts normal cellular function and transport. These changes are accompanied by synaptic dysfunction, inflammation, neuronal injury and progressive loss of brain tissue. The precise causal relationships among amyloid accumulation, tau pathology, neuroinflammation, vascular factors and neuronal degeneration remain subjects of active research.
The simplified idea that Alzheimer's is caused solely by amyloid is therefore incomplete. The disease involves multiple interacting biological processes, and pathological changes can begin many years before clinically obvious dementia. The NHS describes abnormal amyloid and tau accumulation as central features while noting that researchers do not yet fully understand how these proteins produce neuronal loss.
The typical early clinical pattern involves impairment of episodic memory, particularly the ability to retain and retrieve newly learned information. People may repeatedly ask the same questions, forget recent conversations, misplace objects or struggle to remember names and events. As disease progresses, additional cognitive domains become affected, including language, planning, reasoning, visuospatial processing and orientation. Familiar tasks can become increasingly difficult, and later stages may involve loss of independence in dressing, eating, mobility and personal care. Behavioural and psychological symptoms can include anxiety, depression, suspicion, agitation, hallucinations or delusions, although these vary between individuals and stages. The NHS identifies progressive memory impairment followed by broader difficulties in planning, language, orientation and self-care as characteristic of Alzheimer's disease.
Alzheimer's Disease can be divided clinically into stages such as preclinical disease, mild cognitive impairment due to Alzheimer's pathology and Alzheimer's dementia, although boundaries are not always sharp. Biomarker research has expanded the ability to detect amyloid and tau pathology through cerebrospinal-fluid analysis, positron-emission tomography and, increasingly, blood-based biomarkers. These technologies can provide evidence about underlying pathology but require careful interpretation because biomarker positivity does not necessarily mean that a person currently has clinical dementia.
Conversely, clinical diagnosis may remain appropriate when biomarker testing is unavailable. Genetic testing can also provide information about susceptibility, particularly variants such as APOE, but common risk variants do not deterministically establish that an individual will develop Alzheimer's disease. Rare inherited forms involving genes such as APP, PSEN1 and PSEN2 can cause familial early-onset disease.
Risk factors for Alzheimer's Disease include age, genetic susceptibility and several vascular and lifestyle-associated factors. Some risk factors cannot be modified, while others relate to cardiovascular health, physical activity, smoking, diabetes, hypertension, hearing impairment and social or cognitive engagement. Risk reduction is not equivalent to prevention, because no lifestyle programme guarantees that an individual will avoid Alzheimer's disease. Research also distinguishes between observational associations and interventions demonstrated to alter disease incidence.
The complexity of risk reflects the fact that neurodegeneration interacts with vascular health, genetics, brain resilience and ageing. Family history increases risk but does not mean that a person will inevitably develop the disease. Conversely, people without an obvious family history can still develop Alzheimer's disease.
Diagnosis usually combines clinical history, cognitive assessment, physical examination, blood tests to exclude alternative causes and, where appropriate, specialist investigations. Brain imaging can help exclude other conditions and identify patterns consistent with neurodegenerative disease. Biomarker testing is increasingly important in specialised diagnosis and in determining eligibility for certain disease-modifying therapies. The distinction between Alzheimer's pathology and dementia is crucial because dementia can arise from multiple diseases and mixed pathology is common. A person can also have Alzheimer's pathology without yet meeting clinical criteria for dementia. Diagnostic reasoning therefore integrates symptoms, functional change, progression, examination and, when available and appropriate, biomarker evidence rather than relying on a single test.
Treatment historically focused mainly on symptom management, including acetylcholinesterase inhibitors such as donepezil, rivastigmine and galantamine and the NMDA-receptor antagonist memantine for particular stages. These medicines do not reverse established neurodegeneration but can temporarily stabilise or improve some cognitive or behavioural symptoms in appropriate patients.
More recently, disease-modifying antibody therapies directed at amyloid have been developed and authorised in some jurisdictions for selected people with early Alzheimer's disease and confirmed amyloid pathology, although eligibility, availability, monitoring requirements and regulatory status differ between countries. Such therapies can carry significant risks, including amyloid-related imaging abnormalities, making specialist assessment essential. Non-pharmacological management remains important throughout the disease and includes cognitive and functional support, environmental adaptation, treatment of coexisting conditions and assistance for carers.
Alzheimer's Disease is distinct from the broader syndrome of dementia. Alzheimer's pathology is one cause of dementia, while other diseases such as vascular dementia, dementia with Lewy bodies and frontotemporal dementia have different underlying mechanisms. Alzheimer's can also coexist with other pathologies, producing mixed dementia and more complex clinical presentations. A further misconception is that Alzheimer's disease affects memory alone; as it advances, language, judgement, visuospatial processing, behaviour, movement and basic daily functions can become affected.
It is also incorrect to assume that memory loss in older age automatically means Alzheimer's disease because many reversible or non-neurodegenerative conditions can impair cognition. The most accurate model is a progressive neurodegenerative disease with characteristic pathology that commonly produces dementia but can be identified biologically before dementia becomes clinically established.
