Dementia is an umbrella term for a variety of progressive neurological conditions that result in the decline of cognitive abilities. It affects memory, thinking, behavior, and the capacity to carry out everyday tasks. Rather than being a single illness, dementia represents a collection of symptoms caused by different diseases that lead to brain dysfunction, extending beyond the typical effects of aging. According to the National Institute for Health and Care Excellence, dementia involves a set of symptoms that impact intellectual and social functioning to the extent that they interfere with daily life.
Alzheimer’s disease (AD) is the leading cause, accounting for 50–75% of dementia cases. It is characterized by cerebral cortex shrinkage, the build-up of amyloid plaques, and neurofibrillary tangles. Additionally, there is a decline in neurotransmitters—especially those involving the cholinergic system—as well as neuroinflammation. AD frequently coexists with other types, particularly vascular dementia, leading to mixed dementia. In some cases, AD has a genetic basis and tends to appear earlier in life. Neurological exams may appear normal, but brain imaging typically shows significant atrophy in the medial temporal lobes.
Vascular dementia is the second most frequent cause. It results from various underlying vascular issues such as large strokes, multiple small infarcts, or microvascular disease seen post-mortem. Other causes include cerebral amyloid angiopathy and CADASIL (a hereditary condition involving subcortical infarcts and white matter changes). Cardiovascular risk factors like high blood pressure, diabetes, and smoking are often present. It’s commonly linked with strokes or transient ischemic attacks (TIAs) and tends to progress in a stepwise pattern. Like AD, early-onset cases may have genetic origins.
Dementia with Lewy bodies (DLB) accounts for about 10–15% of dementia cases. It is marked by abnormal protein deposits called Lewy bodies in both the cortex and subcortical areas of the brain. DLB shares many features with Parkinson’s disease dementia (PDD). The key distinction lies in the timing of symptoms: if cognitive decline appears before or at least a year before motor symptoms, it is classified as DLB. If motor symptoms begin before or within a year of cognitive changes, it is considered Parkinson’s disease with dementia.
Frontotemporal dementia (FTD) represents a group of conditions and makes up about 2% of all dementia cases. It often runs in families and involves the gradual deterioration of the frontal and/or temporal lobes. Common cognitive screening tools like the MMSE may not detect it, as they typically don’t assess frontal lobe function.
Other less frequent causes of dementia include conditions such as progressive supranuclear palsy, Huntington’s disease, normal pressure hydrocephalus, benign brain tumors, chronic subdural hematomas, and metabolic disorders (e.g., hypothyroidism, Addison’s disease, hypopituitarism). Nutritional deficiencies like low vitamin B12 or thiamine, infections such as HIV and syphilis, autoimmune or inflammatory diseases, and transient epileptic amnesia can also lead to dementia symptoms.
References
NICE (2018) ‘Dementia: assessment, management and support for people living with dementia and their carers’, NG97. Available at: https://www.nice.org.uk/guidance/NG97/ (Accessed: 28 July 2025).
Ladecola, C., et al (2019) ‘Vascular Cognitive Impairment and Dementia’ Journal of the American College of Cardiology, 73(25), pp. 3326-3344.
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