Alzheimer's disease: what it is, symptoms, diagnosis, new treatments and prevention

At first there are small lapses: keys that cannot be found, a missed appointment. Then, slowly, words, orientation and independence are lost. Alzheimer's disease is the most common cause of dementia, and in recent years both the way it is diagnosed and the treatments available have changed. Let us look at what we know today, what can be done and where to turn for help in the United States and the United Kingdom.

What is Alzheimer's disease

Alzheimer's disease is a degenerative disease of the brain: neurons become diseased and die, and with them the circuits that support memory, language, reasoning and behavior are interrupted. It is named after the German physician Alois Alzheimer, who described it in 1906 together with his student from Friuli, Gaetano Perusini.

In the diseased brain, two abnormal proteins build up. The first is beta-amyloid, which is deposited outside the cells, forming the so-called plaques. The second is the tau protein, which clumps into tangles inside neurons. These changes begin many years before the symptoms.

How many people it affects

According to the World Health Organization, in 2021 57 million people worldwide were living with dementia, with nearly 10 million new cases every year; Alzheimer's disease contributes to 60-70% of cases, and dementia is now the seventh leading cause of death in the world.

In Italy, according to estimates from the Istituto Superiore di Sanità (the Italian National Institute of Health) reported by the Italian Ministry of Health on 21 September 2026, about 1.2 million people live with dementia, more than half of them with Alzheimer's disease (about 600,000), and about another 900,000 have a mild neurocognitive disorder. The disease mainly affects people over 65, and women more often.

Causes and risk factors

Alzheimer's disease does not have a single cause. The strongest risk factor is age. True inherited forms, linked to a single gene and often with early onset, are rare: according to the Italian Ministry of Health, dementia cases with a genetic predisposition are 1-2%. More common is the ApoE4 variant of a gene that regulates the transport of fats in the brain: it does not cause the disease, but it increases its likelihood, and today it also matters in the choice of treatment, as we will see.

The 14 modifiable risk factors

In 2024 an international commission of experts updated the list of risk factors that can be acted upon, bringing them to 14. According to their estimates, eliminating them all could prevent or delay up to 45% of dementia cases. They are:

• in early life: less education;
• in midlife: hearing loss, high LDL cholesterol, depression, traumatic brain injury, physical inactivity, diabetes, smoking, high blood pressure, obesity, excessive alcohol;
• in later life: social isolation, air pollution, uncorrected vision loss.

The two new additions compared with 2020 are LDL cholesterol and vision loss. These are population estimates: they show where to act, they do not guarantee anything to the individual.

Symptoms and stages

Symptoms appear gradually and worsen slowly. According to the Italian Ministry of Health, average survival is about 8-14 years from onset.

• Preclinical stage: the changes in the brain are already there, but the person has no symptoms. It can last for years.
• Mild cognitive impairment: memory or another function worsens more than would be expected for age, but the person remains independent. It does not always progress to dementia.
• Mild dementia: recent events are forgotten, the same questions are repeated, people become disoriented in less familiar places and struggle with more complex tasks, such as managing money or medicines.
• Moderate dementia: language difficulties appear, such as losing words, along with confusion about time and place, changes in mood and behavior (anxiety, irritability, suspiciousness) and sleep disturbances. Help is needed with daily activities.
• Severe dementia: the person no longer recognizes family members, loses independence in eating, washing and bladder and bowel control, and becomes completely dependent.

Sleep disturbances and depression can appear early and confuse the picture.

How it is diagnosed

The diagnosis always starts with a medical visit: the account of the person and their family, tests that measure memory, language and attention, blood tests to rule out other causes (for example thyroid problems or vitamin B12 deficiency) and a CT or MRI scan of the brain.

The new criteria: two views compared

In 2024 two documents were published that changed the way the disease is defined.

• The Alzheimer's Association (United States) defines Alzheimer's disease as a biological process: a single abnormal early biomarker is enough to make the diagnosis, even in a person who does not yet have symptoms.
• The International Working Group, a group of international experts, disagrees: most people without symptoms who have positive biomarkers will not become ill in the near future. They should be considered "at risk", and one speaks of disease only when the biomarkers are accompanied by symptoms.

For people who have memory problems, the two positions coincide: the diagnosis must be confirmed with biomarkers.

Biomarkers: cerebrospinal fluid, PET and blood tests

Biomarkers show whether amyloid and tau are present in the brain. The reference tests are:

• cerebrospinal fluid testing: the fluid that surrounds the brain and spinal cord, collected with a lumbar puncture;
• amyloid PET, a nuclear medicine scan that shows the plaques.

The new development of recent years is blood tests, in particular the measurement of p-tau217, a form of the tau protein. In a Swedish study of more than 1,200 patients with cognitive symptoms, a blood test of this type identified the disease with an accuracy of about 90%, compared with 61% for primary care physicians and 73% for specialists who relied on the clinical visit, cognitive tests and CT.

Caution, however. The Alzheimer's Association's 2025 guidelines accept them only in specialist centers, for people who already have cognitive symptoms, and only if the test meets precise accuracy thresholds, which many tests on the market do not meet. In the United States, the Food and Drug Administration (FDA) cleared the first blood test to aid in diagnosing Alzheimer's disease, the Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio, on 16 May 2025, for adults aged 55 and older with signs and symptoms of the disease, and cleared two more blood tests on 19 August 2026. It is the specialist center that decides whether they are needed.

Treatment

Symptomatic medicines

Two types of medicine have been used for many years; they improve symptoms a little but do not stop the disease:

• cholinesterase inhibitors (donepezil, rivastigmine, galantamine), for mild and moderate disease;
• memantine, for moderate and severe disease.

In the United States these medicines are approved by the FDA: according to the National Institute on Aging, cholinesterase inhibitors are prescribed for mild to moderate symptoms, donepezil also for severe disease, and memantine for moderate to severe disease. The benefit is modest: in the large reviews of the studies, donepezil improves a 30-point memory test by about one point after six months, and memantine gives a small benefit in moderate and severe disease. The most common side effects of cholinesterase inhibitors are nausea and diarrhea.

Anti-amyloid antibodies: lecanemab and donanemab

They are the first medicines that remove amyloid from the brain. They are given into a vein, in a hospital or infusion center. In the United States, the current lecanemab label (revised July 2026) also includes a once-weekly injection under the skin with an autoinjector (Leqembi Iqlik).

• Lecanemab (Leqembi): granted accelerated approval by the FDA on 6 January 2023 and traditional approval on 6 July 2023; licensed in the United Kingdom by the Medicines and Healthcare products Regulatory Agency (MHRA) on 22 August 2024. In the main study, of 1,795 people, after 18 months it slowed worsening by less than half a point on a severity scale from 0 to 18 compared with placebo.
• Donanemab (Kisunla): approved by the FDA on 2 July 2024; licensed in the United Kingdom by the MHRA on 23 October 2024. In the main study, of 1,736 people, the slowing on the same scale was about 0.7 points at 76 weeks.

In the United States, the FDA-approved prescribing information says that treatment should be started in people with mild cognitive impairment or mild dementia due to Alzheimer's disease, after confirming amyloid. It does not exclude people with two copies of ApoE4, but a boxed warning states that they have a higher risk of the main side effect and that ApoE4 testing should be done before starting treatment. In the United Kingdom, the MHRA has licensed both medicines only for adults in the early stages of Alzheimer's disease who have one or no copies of ApoE4.

This effect is called ARIA: swelling (edema) or small bleeds in the brain, visible on MRI. It often causes no symptoms, but it can be serious. In the studies, edema was seen in 12.6% of patients on lecanemab and in 24.0% on donanemab. For this reason an MRI is needed before starting and further MRIs at set times during treatment. In the United Kingdom they must not be used in people taking anticoagulants (blood thinners) or with cerebral amyloid angiopathy on MRI before starting. In the United States, the label advises caution in people who need anticoagulants, and the trials excluded people with a previous brain bleed larger than 1 cm or more than 4 microbleeds.

And who pays for them? In the United States, after the traditional approval of lecanemab, the Centers for Medicare & Medicaid Services (CMS) announced on 6 July 2023 that Medicare covers these medicines for people with mild cognitive impairment or mild Alzheimer's dementia with documented amyloid, provided their doctor takes part in a qualifying registry that collects data on the treatment (national coverage determination 200.3). In the United Kingdom, the National Institute for Health and Care Excellence (NICE) has not issued final guidance: its latest draft guidance does not recommend lecanemab for NHS use, and on 29 and 30 July 2026 NICE paused the evaluations of lecanemab and donanemab while the companies and NHS England hold commercial discussions. This information comes from the FDA, CMS, MHRA and NICE, consulted on 21 October 2026: check with your doctor what applies in your case.

When family members ask me about the new antibodies, I explain that they are a real but small step forward: they slow the disease, they do not stop it, and they are suitable only for some people in the early stages.

Non-drug treatments and support for caregivers

Cognitive stimulation, that is, group activities that train memory, attention and language, slightly improves cognitive abilities, communication and quality of life, according to a review of 37 studies. Physical activity, regular routines and a safe home also matter.

Caregivers carry an enormous burden: according to the WHO, about half of the global costs of dementia is care provided by family members, who devote an average of 5 hours a day to it. Training courses for family members, support groups and day centers help them cope over time.

Can it be prevented?

There is no sure way to avoid Alzheimer's disease, but the risk of dementia can be reduced by acting on the 14 factors: controlling blood pressure, blood sugar and cholesterol, not smoking, limiting alcohol, staying active, treating depression, using a hearing aid if needed, correcting vision and keeping an active social life. On diet, the Italian edition of Med4Care has an article on the MIND diet.

When to see a doctor

It is worth talking to your primary care doctor when forgetfulness gets worse over a few months, you get lost on familiar streets, you struggle to manage money or medicines, or your family notices a change in personality. The doctor assesses the situation and, if needed, refers you to a specialist in diagnosing dementia, for example in a memory clinic, or suggests a geriatric assessment. Some memory problems have treatable causes: it is better not to wait.

Where to find help in the United States and the United Kingdom

• Alzheimer's Association 24/7 Helpline (United States): 800.272.3900, around the clock, 365 days a year, with interpreters in more than 200 languages (alz.org).
• ADEAR Center of the National Institute on Aging (United States): the public information and referral service on Alzheimer's disease, 800-438-4380, in English and Spanish, Monday to Friday, 8:30 a.m. to 5:00 p.m. Eastern Time (nia.nih.gov).
• Alzheimer's Society Dementia Support Line (United Kingdom): 0333 150 3456, Monday to Wednesday 9 a.m. to 8 p.m., Thursday and Friday 9 a.m. to 5 p.m., Saturday and Sunday 10 a.m. to 4 p.m. (alzheimers.org.uk).
• Emergencies: call 911 in the United States or 999 in the United Kingdom.

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