Introduction

Understanding the differences between mixed dementia and Alzheimer's disease requires recognising what dementia is and its connection to Alzheimer's disease. This article will explain what dementia is, its common symptoms, and its types. It will also discuss Alzheimer's disease and its symptoms. The later sections focus on mixed dementia, explaining what it is and identifying its common types. By the end of this article, you should have a clear understanding of what "dementia" means, as well as a deeper understanding of Alzheimer's disease and its relationship to mixed dementia.

Dementia

Dementia is not a specific disease; rather, it is a syndrome or a group of symptoms associated with various underlying conditions. It is generally characterised by a decline in cognitive skills, such as memory, thinking, and reasoning. In more severe cases, patients may also experience communication difficulties, changes in mood and behaviour, or impaired judgement, leading to a reduced ability to perform everyday tasks.^1,2

Symptoms of dementia

• Emotional Disturbances: Depression, anxiety, apathy, elated mood, euphoria, irritability
• Abnormal Thoughts: Delusional ideas (e.g., believing that a spouse is an impostor)
• Perceptual Disturbances: Visual hallucinations
• Motor Function Disturbances: Slowed movements and speech, hyperactivity (increased movement and energy), agitation (physically or verbally aggressive or non-aggressive behaviours)
• Sleep Rhythm Changes: Hypersomnia, insomnia, sleep-wake cycle reversal, fragmented sleep
• Changes in Appetite and Eating Behaviours: Appetite changes, anorexia, hyperphagia, changes in food preferences²

Major types of dementia

Alzheimer’s disease

Alzheimer’s disease is the most common type of dementia. It is characterised by a gradual decline in cognitive abilities and a progressive loss of memory.

Vascular dementia

Vascular dementia is caused by cerebrovascular disease and brain infarcts. While it shares similarities with Alzheimer’s disease, such as cognitive decline and memory loss, patients with vascular dementia may also experience depression and anxiety.

Dementia with lewy bodies

Lewy bodies are abnormal protein deposits in the brain that cause visual hallucinations and delusions, leading to Lewy body dementia.

Frontotemporal lobar degeneration

Frontotemporal lobar degeneration can be further divided into subtypes, such as frontotemporal dementia, semantic dementia, and progressive aphasia. All types of frontotemporal lobar degeneration are characterised by changes in behaviour, social awareness, and appetite.²

Diagnosis

A single test cannot diagnose dementia. Usually, diagnosis involves a combination of medical history, physical examination, laboratory testing, and assessment by a general practitioner (GP). The GP’s examination also focuses on changes in thinking, everyday functioning, and behaviour. In most cases, determining whether a patient has dementia is not the most challenging part of the process; the real challenge lies in identifying the specific type of dementia. Symptoms and structural changes in the brain often overlap, making it difficult to pinpoint a particular type. Therefore, it is not uncommon for someone to receive a dementia diagnosis without a specified type.⁹

Alzheimer's disease

As mentioned earlier in this article, Alzheimer’s disease is a type and a cause of dementia. It is a brain disorder that gradually impairs memory and thinking skills, eventually leading to an inability to complete even the simplest everyday tasks (see Figure 1).^3,5 Alzheimer’s disease is caused by the accumulation of beta-amyloid protein around neurones, which causes the death of the neurones and damage to brain tissue.

Figure 1

Progression of Alzheimer’s disease. The lengths of stages vary and can differ between patients.⁵

Risk factors

Age

In most cases, Alzheimer’s disease appears later in life, but it is not a normal part of ageing. Additionally, older age alone is not a cause of Alzheimer's disease. According to data from Hebert et al. (2013), 5% of people between the ages of 65 and 74 have Alzheimer’s disease. For those aged 75 to 84, the risk increases to 13.2%, and for those aged 85 and older, the risk rises to 33.4%.⁵

Family history

A family history of Alzheimer’s disease is not necessary for someone to develop the condition. However, there is an increased risk for those who have a first-degree relative (such as a sibling or parent) with Alzheimer’s disease. The risk increases further for those who have more than one first-degree relative with Alzheimer’s disease.^5,6

Genetics

The risk of developing Alzheimer’s disease is also influenced by genetic factors. As of 2024, there are over 30 genes known to affect biological processes that increase the risk of Alzheimer’s disease. Of these, the APOE-e4 gene has the greatest impact on the risk of dementia in older age. This gene provides information for a protein used to transport cholesterol in the bloodstream. However, carrying the APOE-e4 gene does not guarantee that a person will develop Alzheimer’s disease. Each person inherits one of three possible alleles (forms) of the APOE gene from each parent. The forms are e2, e3, e4, thus there are six possible APOE gene pairs: e2/e2, e3/e3, e4/e4, e2/e3, e2/e4, e3/e4. Inheriting one copy of the e4 gene increases the risk of developing Alzheimer’s disease, while inheriting two copies (e4/e4) further elevates this risk. In contrast, carrying an e2 copy decreases the risk, while e3 copies do not have any known impact on Alzheimer’s disease.^4,5

Other risk factors

While age, family history, or genetic predispositions for Alzheimer’s disease are factors that cannot be controlled, there are other factors that can decrease the likelihood of developing Alzheimer’s disease.

Cardiovascular health

There is a close connection between heart health and brain health. Therefore, maintaining a healthy heart increases the likelihood of a healthy brain. Conditions such as high blood pressure, diabetes, or smoking negatively affect the heart and, in turn, increase the risk of developing Alzheimer’s disease.^5,12

Education

A large body of research supports the claim that people with more years of formal education are less likely to develop Alzheimer’s disease. Engaging in learning promotes cognitive activity, which can delay the development of Alzheimer’s disease symptoms.^5,13,14

Social and cognitive engagement

Studies also suggest that being social and participating in activities that increase cognitive functioning improve brain health, thereby reducing the risk of Alzheimer’s disease.^5,15

Treatment

Currently, Alzheimer’s disease is incurable. However, patients can receive medications to help reduce symptoms. A common type of medication used for this purpose is acetylcholinesterase (AChE) inhibitors. They work by increasing acetylcholine levels in the brain, resulting in improved nerve cell communication. Another type of medication is memantine which works by blocking excessive amounts of glutamate (chemical) in the brain. In the later stages of any type of dementia, behavioural and psychological difficulties such as anxiety, aggression, or hallucinations may occur. For this reason, patients are often prescribed antipsychotic medications as well. 

In addition to medications, patients with Alzheimer’s disease can take part in supporting activities such as cognitive stimulation therapy (CST). CST consists of group activities and exercises used to improve memory and problem-solving skills. Cognitive rehabilitation focuses on using functioning parts of the brain to achieve everyday tasks. Visual and auditory aids, such as photos and music, can help in recalling past life events through reminiscence (talking about the past) or life story work. While these activities do not cure Alzheimer’s disease, there is evidence to suggest they may improve mood and well-being.⁷

Mixed dementia

Mixed dementia occurs when there is more than one cause for the changes in a patient's brain. In most cases, it involves a combination of Alzheimer’s disease and another type of dementia. Mixed dementia is a very common disorder, affecting about 22% of elderly people diagnosed with Alzheimer’s disease. However, it is difficult to diagnose due to the fact that the symptoms of different types of dementia often overlap. In most cases, people are unaware they have mixed dementia until after death when an autopsy is performed.^5,8

Frequent types of mixed dementia

Alzheimer’s disease & vascular dementia

Alzheimer’s disease often occurs alongside vascular dementia, which can be further divided into different types, as listed below. 

Alzheimer’s disease & multiple infarcts

In this type, multiple large strokes affect various parts of the brain, while Alzheimer’s disease further contributes to brain impairment.  

Alzheimer’s disease & subcortical arteriosclerotic encephalopathy

Small strokes occur deep in the brain, in areas such as the basal ganglia, thalamus, and sometimes the white matter. At the same time, Alzheimer's disease also affects the brain.

Alzheimer’s disease & strategic infarct dementia

This condition involves strokes that affect either both sides of the thalamus or both the thalamus and hippocampus, while Alzheimer’s disease simultaneously impacts the brain.^10,11

Other combinations of dementia

Different types of dementia can overlap. However, Alzheimer's disease is often combined with some form of vascular dementia.¹⁰

Summary

In summary, the term “dementia” refers to a group of conditions characterised by a decline in cognitive skills. There are many different types of dementia, one of which is Alzheimer’s disease. Additionally, various types of dementia can coexist, a condition known as mixed dementia. The most common form of mixed dementia is Alzheimer’s disease combined with a type of vascular dementia.