What is Alzheimer's disease?
Alzheimer's disease is a progressive neurodegenerative disease characterized by the progressive loss of nerve cells in the brain. Pathologically, two forms of deposit are characteristic:
- Beta-amyloid plaques: Extracellular deposits of a fragment of the amyloid precursor protein. They often develop decades before the first clinical symptoms.
- Tau fibrils (neurofibrillary tangles): Intracellular deposits of a misfolded protein that normally stabilizes the supporting structure of the nerve cells. Tau pathology correlates more closely in time with the clinical symptoms than amyloid.
The consequence is a progressive cell death that initially affects the hippocampus (memory) and then, over a large area, the cerebral cortex. The clinical picture follows this spread: short-term memory first, then orientation, language, ability to act, personality.
→ For an overview of all forms of dementia and how they are distinguished: Dementia in old age.
- Germany today: Around 1.2 million people with Alzheimer's (about two thirds of all dementia cases).
- Prevalence by age: Rare under 65 years of age (early-onset Alzheimer's); from 65 on, the frequency roughly doubles every five years.
- Sex ratio: Women are somewhat more frequently affected, partly explained by higher life expectancy, partly by independent biological factors.
- Familial forms: Fewer than 1 percent of all cases are monogenetically inherited (mutations in the APP, PSEN1 or PSEN2 gene); these typically manifest before the age of 65.
- Genetic risk factors: The apolipoprotein E gene (APOE) — especially the ε4 variant — considerably increases the risk, but is not a causal gene in the strict sense.
Symptoms and course: the three phases
The course of Alzheimer's can be roughly divided into three phases, which in individual cases can be of different lengths — from a few years to more than fifteen years between the first symptoms and the end of life.
Everyday life can still largely be managed independently, but changes become noticeable — first for the family, later for the affected people themselves. Frequently, symptoms appear that also occur in mild cognitive impairment (MCI):
- Frequent word-finding difficulties
- Short-term memory gaps — what has just been experienced is not retained
- Decline in the ability to concentrate, especially with new or complex tasks
- Uncertainty in unfamiliar surroundings
- Occasional orientation problems in time and space
- A tendency toward social withdrawal out of being overwhelmed
Independence becomes increasingly restricted, the need for help rises noticeably. In this phase, a distinction from depression in old age is also important, since both diseases can manifest in listlessness and withdrawal:
- Marked memory disorder, also for biographical content
- Orientation problems in the familiar home
- Difficulties with everyday activities (dressing, preparing food, personal hygiene)
- Personality changes, mood swings, sometimes aggressive episodes
- Sleep-wake rhythm disorders, nocturnal wandering
- Individual behavioral abnormalities (restlessness, fidgeting, repetitive actions)
Complete need for care in all areas of life. In this phase, complications such as aspiration pneumonia and immobility frequently occur:
- Extensive loss of the ability to speak
- Failure to recognize close relatives
- Complete incontinence
- Gait disorders, later being bedridden
- Swallowing disorders — a frequent cause of aspiration pneumonia
- Wakefulness, but without a meaningful reaction to the environment
The average survival time after diagnosis is, depending on age and comorbidities, 7 to 10 years, with great individual variation. In most cases, the cause of death is not Alzheimer's disease directly, but a pneumonia or other infection in the terminal stage.
Diagnosis: the path to a reliable classification
Modern Alzheimer's diagnostics are considerably more precise than ten years ago. It proceeds in three steps. A complete geriatric assessment frequently forms the basis here:
- Clinical testing: MMSE, MoCA, clock-drawing test, DemTect — validated short tests to quantify cognitive deficits.
- Imaging: MRI or CT to depict the typical atrophy (especially of the hippocampus) and to rule out other causes (haemorrhages, tumors, normal-pressure hydrocephalus).
- Biomarkers: Lumbar puncture with determination of beta-amyloid 1-42, total tau and phospho-tau. Alternatively, amyloid or tau PET. Blood-based biomarkers (plasma-based p-tau217) have been validated in studies since 2024 and are entering clinical routine.
Biomarker-supported diagnosis today, in specialized centers, allows Alzheimer's disease to be distinguished from other forms of dementia with more than 90 percent certainty — a precision that ten years ago was only achievable post mortem. The differential diagnosis between dementia and depression also plays an important role.
→ The complete diagnostic pathway at a glance: Dementia diagnostics — from the clock-drawing test to biomarker analysis.
Therapy: what helps with Alzheimer's?
The treatment of Alzheimer's disease rests on four pillars. None of them alone is sufficient — the interplay makes the difference. The section on geriatrics and the medicine of aging also provides a comprehensive overview.
- Cholinesterase inhibitors: Donepezil, rivastigmine, galantamine. Approved for mild to moderate Alzheimer's dementia. They typically slow the progression by six to twelve months but are not a cure. Most frequent side effects: nausea, diarrhea, sleep disorders.
- Memantine: NMDA receptor antagonist. Approved for moderate to severe Alzheimer's dementia. Often in combination with a cholinesterase inhibitor.
When medicating older patients, the topic of polypharmacy in old age must also be taken into account — interactions of several simultaneously taken medications can complicate the therapy. Targeted deprescribing of unnecessary medications is therefore an important component of modern geriatric medicine.
Lecanemab and donanemab are new monoclonal antibodies that specifically break down beta-amyloid in the brain. In studies relevant to approval (CLARITY-AD, TRAILBLAZER-ALZ 2), they showed a slowing of the clinical course by 27 to 35 percent over 18 months in patients with early Alzheimer's disease.
Important for classification:
- Suitable only for patients with mild cognitive impairment or mild Alzheimer's dementia
- The prerequisite is biomarker evidence of an amyloid pathology
- Contraindications are certain genetic constellations (two copies of the APOE-ε4 variant) and pre-existing conditions such as microhaemorrhages
- Regular MRI checks are mandatory because of possible amyloid-related imaging abnormalities (ARIA) — cerebral edema and microhaemorrhages
- Treatment only in specialized centers with appropriate expertise
These therapies are not a miracle cure, but a first step in a long therapy development. The slowing is real, but moderate. A cure is still not possible.
- Cognitive stimulation (CST): Structured group programs with effects comparable to anti-dementia drugs.
- Physical activity: Aerobic training and strength training slow progression and improve mood. In older patients, fall prevention is also a central topic.
- Social participation: Loneliness is an independent risk factor for progression.
- Nutrition: The Mediterranean or MIND diet shows protective effects in cohort studies. Malnutrition in old age demonstrably has a negative effect on the cognitive course.
- Correcting hearing and vision aids: Uncorrected hearing loss is, according to the Lancet Commission 2024, one of the greatest modifiable risk factors for dementia progression.
- Sleep hygiene: Healthy sleep has its own role in the breakdown of amyloid — the so-called glymphatic clearance.
Accompanying symptoms such as depression, sleep disorders, restlessness and psychotic symptoms are treated individually — with particular caution toward neuroleptics, which increase the mortality risk in Alzheimer's patients and should be used only briefly and at the lowest dose. A delirium in older people, too, can acutely worsen the course and requires targeted delirium prevention.
→ In detail on the current dementia therapy landscape: Dementia therapy 2026.
Living with Alzheimer's: what relatives need to know
- Early provisions: A lasting power of attorney, advance directive and care directive should be drawn up while there is still full legal competence.
- Care level: The application to the Medical Service explicitly takes cognitive impairments into account. A care level opens access to benefits and relief.
- Daily structure: Regular routines, familiar objects, clear visual orientation (clock, calendar) reduce anxiety and restlessness.
- Communication: Short sentences, eye contact, patience. Do not correct when it is not necessary. So-called validation — acknowledging the emotional content of what is said rather than insisting on reality — is often more effective than fidelity to the truth.
- Self-help and relief: Caring relatives have an increased risk of depression and exhaustion. Day care, short-term care and self-help groups are not a weakness but a structural prerequisite for sustainable care. Early geriatric rehabilitation can help to preserve existing abilities for as long as possible.
When should you see a doctor?
The earlier the diagnosis is made, the more options remain. Concrete occasions:
- Repeated forgetting that noticeably impairs everyday life
- Recurrent orientation problems in familiar surroundings
- Word-finding difficulties and changes in the ability to speak
- Personality changes or social withdrawal
- Uncertainty in financial or administrative matters
- Conflicts between relatives over the assessment of the situation
The first point of contact is the general practitioner, who, if there is a suspicion, refers the patient to a neurologist, a memory clinic or a geriatrician. For an early assessment of the risk, a frailty screening can also be worthwhile, since frailty syndrome is closely linked to the dementia risk. The combination of specialized neurological diagnostics and geriatric assessment is particularly valuable in multimorbid older patients.
→ How a comprehensive geriatric assessment works: Geriatric assessment.
