Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative condition that gradually erodes memory, language, judgement, and eventually basic function. It is the most common cause of dementia worldwide, accounting for roughly 60 to 70 percent of cases.

It is named after Alois Alzheimer, who in 1906 described the case of Auguste Deter and the abnormal protein deposits in her brain at autopsy.

What happens in the brain

Two hallmark pathologies define Alzheimer's:

• Amyloid plaques, which are extracellular clumps of beta-amyloid protein
• Neurofibrillary tangles, which are intracellular accumulations of misfolded tau protein

These appear years before symptoms and spread in a characteristic pattern. The hippocampus is one of the earliest affected regions, which is why memory problems are usually the first symptom.

Over time the disease produces widespread cortical atrophy, especially in temporal and parietal regions.

How it's diagnosed

There is no single test. Diagnosis combines:

• Clinical history and cognitive testing, often using the MoCA or MMSE
• MRI to assess atrophy patterns and exclude other causes
• Increasingly, biomarkers from CSF or PET imaging (amyloid and tau)
• Genetic factors like APOE4 status in some cases

Early signals

Mild cognitive impairment is often the first clinically detectable stage. Brain age estimation from MRI can show accelerated brain ageing years before symptoms appear.

Treatment

There is no cure. Cholinesterase inhibitors and memantine offer modest symptomatic benefit. Newer monoclonal antibodies that target amyloid (lecanemab, donanemab) slow progression modestly in early disease.

Modifiable lifestyle factors known to lower risk include cardiovascular health, education, social engagement, regular exercise, and sleep quality. Several of these also lower the brain age gap.