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Alzheimer’s Disease | Definition, Causes, Diagnosis & Treatment

Alzheimer’s Disease (AD) is the most common form of dementia worldwide (60-70% of all dementia cases) and is a progressive neurodegenerative disorder. Though around 10-15% of cases are genetic, the vast majority of cases are sporadic and attributed to many risk factors. There is, at present, no cure or disease-modifying treatments for Alzheimer’s disease.

What is Alzheimer’s Disease?

Alzheimer’s disease (AD) accounts for around 60% of all dementia cases worldwide, making it the most common form of dementia. Alzheimer’s is a progressive neurodegenerative disease with symptoms gradually worsening over a period of a few years. As with most dementias, Alzheimer’s symptoms usually begin with subtle difficulties in remembering recent memories before gradually progressing to more severe symptoms (outlined below).

Alzheimer’s is generally a disease of advanced age and becomes more common over the age of 65. However, developing dementia is not a normal or healthy part of ageing. In rarer cases, Alzheimer’s can affect individuals much younger (between 30-40 years old) with approximately 5% of cases occurring in people under the age of 65. Though the disease is the same, the causes of early-onset Alzheimer’s are usually slightly different to what is known as sporadic Alzheimer’s disease.

Irrespective of the exact cause of Alzheimer’s, which is still poorly understood, two key pathological hallmarks are key to Alzheimer’s: amyloid plaques and tangles (discussed in detail later). Over time, these abnormal proteins contribute to the death of neurons leading to a generalised shrinkage of the brain (cortical atrophy), which leads to the symptoms of Alzheimer’s, as well as death within 9 years after symptoms start.

Alzheimer’s Disease Signs & Symptoms

As Alzheimer’s disease is a progressive neurodegenerative disease, symptoms are initially subtle and mild, before gradually worsening over a period of several years. The onset, progression severity and speed, as well as time to death varies significantly between affected individuals, depending on the exact cause and mechanism involved.

The symptoms of Alzheimer’s disease can be broken down into three stages:

1. Early-Stage Symptoms:

  • Subtle memory loss of the most recent events e.g. forgetting a recent conversation or event, as well as repetitive questioning and the inability to select certain words in conversations
  • Subtle mood changes or behavioural changes which are not normal for the individual – these can manifest as increased anxiety and confusion
  • Other cognitive symptoms may include increased difficulty in making decisions and becoming more hesitant in certain things

It is important to note that misplacing items or forgetting things occasionally is a normal part of ageing – however, when this becomes routine, is often a sign of dementia.

2. Middle-Stage Symptoms:

  • Worsening of memory loss which progresses to forgetting names of people close to them, as well as forgetting the faces of loved ones
  • Mood changes become more profound with increased anxiousness, frustration and signs of repetitive or impulsive behaviours
  • Depressive symptoms alongside anxiety – including loss of motivation
  • In some cases, there may be signs of delusions and hallucinations
  • Insomnia and disturbed sleep patterns are common
  • The emergence of motor difficulties including aphasia (speech problems)

At this stage, activities of daily living become impaired and patients usually require some level of care and assistance, especially as the disease progresses.

3. Late-Stage Symptoms:

  • All of the above symptoms become more severe, behavioural, mood, motor and cognitive – with increased distress for both the patient and caregiver
  • Violence towards caregivers is not uncommon and patients can become suspicious of those around them, including loved ones
  • Due to feeding issues, severe weight loss can occur in some patients
  • As motor problems worsen, there may be severely impaired speech, difficulty in positioning oneself, urinary and bowel incontinence

At this stage, activities of daily living become severely impaired and patients usually require full-time care and assistance. Patients become more withdrawn from life and symptoms decline eventually leading to death.

In a lot of cases, the progression of disease course can be enhanced by other factors independent of Alzheimer’s pathology. These include infections, strokes, head injuries and delirium. Sometimes, certain medications can also worsen the symptoms of dementia. In general, death occurs anywhere from 3-9 years after the first symptoms appear.

There is much overlap between symptoms of Alzheimer’s disease and other forms of dementia. It is also common for patients with Alzheimer’s over the age of 65 to also experience symptoms and pathology of vascular dementia, which often initially manifests with more marked motor impairment.

Causes of Alzheimer’s Disease

The exact cause of the majority of Alzheimer’s cases (sporadic) is still not fully known, however, around 5-10% of all cases are due to genetic differences, which are now well characterised.