Dementia: what are the causes ?


Dementia is not a disease, but rather a sum of symptoms with very diverse origins.

There are more than 50 diseases, or infectious and toxic agents which, by affecting the brain, cause dementia.


Dementia affects 5% of people aged 65 and over and around 40-50% of those over 85.

The main causes of dementia

CausesTypes of dementia
Alzheimer’s diseaseAlzheimer-type dementia
• Pick’s disease
• Frontal degeneration
Frontotemporal dementias
Lewy bodyDementia with Lewy bodies
Primary progressive aphasiaDementia linked to cortical atrophy
• Parkinson’s disease
• Huntington’s disease
Subcortical dementia
• Cardiovascular diseases (cerebrovascular accident, arteriosclerosis)
• Binswanger’s disease
Vascular dementias including:
• Single or multiple infarct
dementia • Subcortical vascular dementia
• Chronic subdural hematoma
• Brain tumors
• Normal pressure hydrocephalus
• Head trauma
Dementias related to neurological conditions
• Syphilis
• Viral encephalopathy (Creutzfeldt-Jakob, Gerstmann-Straussler-Scheinker diseases)
• Meningitis
Dementia associated with infection
• Vitamin B6, B12 or folic acid deficiency
• Hypo or hyperthyroidism
• Alcoholism
• Heavy metals (mercury, lead)
• Drugs or drug intoxication
• Dehydration, hyperthermia
Metabolic or toxic agent-related dementias

Dementia subgroups

The medical community divides dementia into two subgroups based on their causes:

  • Degenerative dementias: Alzheimer’s disease, Lewy body dementia, frontotemporal lobar dementia (degeneration), dementia associated with Parkinson’s disease or extrapyramidal syndrome
  • Secondary dementias: vascular dementia, neurosyphilis, hypothyroidism, normal pressure hydrocephalus, central nervous system infections, meningitis, encephalitis, HIV, metabolite or toxic attacks (alcohol), Creutzfeldt-Jakob disease.

The causes can be reversible (depression, delirium, harmful side effects of drugs, infections, etc.) or irreversible (dementia of the Alzheimer type, vascular dementia, frontotemporal dementia, dementia with Lewy bodies, dementia associated with Parkinson’s disease, etc.).

The prevalence of dementias

Dementia of the Alzheimer type is the most common dementia (accounting for approximately 50% to 70% of cases), followed by vascular dementia (approximately 20%) and dementia with Lewy bodies. Vascular dementia is often associated with dementia of the Alzheimer type: we then speak of mixed dementia.

Before the age of 65, half of dementia is due only to Alzheimer’s disease, reaching 70% after the age of 65. 

 Alzheimer’s diseaseDementia with Lewy bodiesFrontotemporal dementiasVascular dementia
Prevalence 50-70%0-25%8-10%15-30%

The treatment of dementia

There is currently no cure for most dementias (such as Alzheimer’s disease). However, cognitive symptoms are treated by alleviating them and/or delaying their progression.
It is sometimes possible to treat or reduce non-cognitive symptoms (aggressiveness, agitation, sleep disturbances, depression, hallucinations, etc.) using medication or by modifying the living environment (for example lowering the sound and light level in the House).
Some dementias are treatable, such as those linked to a vitamin B deficiency or following alcoholism.

The anatomical location of dementias

Some of these dementias primarily affect either the cortical areas or the areas located under the cortex (subcortical areas); they can, as in the case of vascular dementia, affect both.

Symptoms associated with dementia

Their nature, severity and progression differ depending on the type of dementia.  For example, the symptoms associated with dementia with Lewy bodies (Lewy bodies are cells that ubiquitously affect the brain) resemble those of Alzheimer’s disease (memory loss, difficulty speaking, etc.) but generally progress faster. Behavioral disorders appear earlier and more often in frontotemporal dementia or Lewy body dementia than in Alzheimer-type dementia or vascular dementia.

Clinical characteristics of dementias

The discovery of biomarkers or the contribution of neuroimaging (e.g., MRI, scanner) made it possible to confirm the clinical diagnosis of each of the tomes of dementia.

 Alzheimer’s diseaseDementia with Lewy bodiesFrontotemporal dementiasVascular dementia
First signsInsidious cognitive losses (short-term memory)Insidious cognitive and behavioral disturbances (hallucinations)Behavioral and language disorders, apathy, disinhibitionSudden onset (with neurological disorder for example)
EvolutionprogressiveprogressiveprogressiveStepwise worsening
Accompanying signs Motor disorders, hallucinations, hypersensitivity to neurolepticsCompulsive behaviors, irritability, physical neglectCardiovascular diseases, cerebrovascular history, focal neurological deficit
Profile of DisordersSignificant memory disordersAttention disorders (beginning forms)Alterations in executive functions, attention disorders (beginning forms)Variable (beginner forms)
NeuroimagingTemporal lobe involvementInvolvement of cortical and subcortical regionsLocalized frontal or temporal atrophyCerebrovascular lesions