Dementia due to multiple underlying processes
Mixed dementia occurs when a person’s dementia symptoms reflect multiple disease processes interacting together. The combination may progress differently than either condition would on its own.
What is mixed dementia?
Mixed dementia describes a situation where more than one disease process is affecting the brain at the same time, rather than a single, distinct disease.
Because more than one process is involved, symptoms often reflect a mix of features from each underlying condition. For example, a person may experience the prominent short-term memory loss typical of Alzheimer’s disease, alongside slowed thinking, planning difficulties, or gait changes typical of vascular dementia. The pattern and pace of decline can also differ from what would be expected with either condition alone, sometimes progressing more quickly or unevenly.
Mixed dementia is thought to be more common than it is diagnosed during life, especially in late-onset dementia. Studies examining brain tissue after death suggest that combined pathology is frequently present, even when only one type of dementia was diagnosed clinically.
Over time, mixed dementia can lead to symptoms including:
- memory loss
- movement, balance or gait issues
- personality or mood changes
- reduced independence with everyday tasks
- trouble concentrating.
What happens in the brain?
Mixed dementia involves more than one disease process occurring together in the brain. Most commonly, this includes a build-up of abnormal amyloid and tau protein (the changes seen in Alzheimer’s disease) together with:
- damage to the brain from blood vessel disease (the changes seen in vascular dementia)
- other pathologies (eg a build-up of alpha-synuclein protein as seen in Lewy body dementia)
- the effects of other more general medical problems.
When more than one of these processes is present, they can interact, sometimes making symptoms more complex or affecting how the condition progresses over time.
What increases the risk of mixed dementia?
Because mixed dementia involves more than one underlying disease process, its risk factors are largely a combination of those for each contributing condition.
Factors that can’t be changed include:
- age – the strongest risk factor overall. Mixed dementia becomes more common with increasing age, particularly beyond the mid-70s and 80s
- family history and genetics – a family history of Alzheimer’s disease, stroke, or vascular disease, or general medical conditions can contribute to risk
- prior stroke – having had one or more strokes, including small 'silent' strokes, increases the vascular contribution to mixed dementia.
Which risk factors may be modifiable?
Factors that may be modifiable, meaning they can potentially be reduced through lifestyle or medical care, include:
- cardiovascular health – high blood pressure, diabetes, high cholesterol and smoking all increase the vascular contribution to mixed dementia, in the same way they increase risk of vascular dementia specifically
- head injury – a history of significant head injury is generally associated with a higher risk of dementia
- hearing loss, social isolation and reduced mental stimulation – all associated with a higher overall dementia risk, including mixed presentations
- physical activity – regular exercise is associated with a lower risk of both the vascular and Alzheimer’s contributions to dementia.
Mixed dementia reflects the combined effect of more than one disease process. Managing modifiable risk factors, particularly cardiovascular health, is often considered especially important, as it may help limit the vascular contribution even where an Alzheimer’s-type process is also present.
Common patient questions
Yes, mixed dementia occurs when more than one disease process contributes to cognitive decline.
It is a combination. Mixed dementia means two or more recognised contributors to dementia are present together, rather than being a separate disease in its own right.
Diagnosis relies on the same combination of history, cognitive testing and brain imaging used for other types of dementia, looking for evidence of more than one contributing factor.
Not necessarily, it varies from patient to patient.
Because the features of each underlying condition can overlap, and current tests cannot always clearly separate the individual contributions of each disease process.
In many cases, the presence of more than one process is only confirmed when brain tissue is examined after death.
It can. Management often addresses each contributing condition. Your specialist will tailor treatment to the conditions that are contributing.