What causes dementia?

Updated: Sep 19, 2018
  • Author: Richard D Shin, MD; Chief Editor: Gil Z Shlamovitz, MD, FACEP  more...
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Dementia can occur primarily, or can be secondary to cerebrovascular disease, chronic CNS infection, CNS trauma, increased ICP (eg, neoplasia, mass effect, hydrocephalus), toxins, avitaminosis, autoimmune disease, and psychiatric illness.

Primary dementias include Alzheimer disease and frontotemporal dementia (FTD). AD accounts for up to 90% of all primary dementias and more than 50% of all dementing illnesses.

FTD is highly familial, presents at a younger age than Alzheimer disease, and is associated with profound personality changes, social incompetence, and stereotypical behaviors, yet with preserved visuospatial skills. The brain invariably shows a severe and asymmetric atrophy of the frontal and temporal lobes with only rare involvement of the parietal or occipital lobes associated with sparing of the posterior two thirds of the superior temporal gyrus. A thin, knife-edge appearance of the gyri is often seen secondary to the severe atrophy present in Pick disease, a subtype of FTD. The typical pattern of atrophy is often prominent enough to distinguish Pick disease from Alzheimer disease macroscopically.

Some forms of Alzheimer disease are thought to have a genetic or familial basis. This is particularly true of Alzheimer disease that begins at a relatively young age and follows a fulminant course.

Alzheimer-like dementia is seen in 40% of patients with Parkinson disease and in a very high percentage of patients with Down syndrome who live long enough to develop Alzheimer disease.

Cerebrovascular causes include lacunar stroke syndrome (multi-infarct dementia), thalamic stroke, and vasculitides as seen in systemic lupus erythematosus and other rheumatologic disorders.

Infectious causes of dementia include HIV, Creutzfeldt-Jakob disease, neurosyphilis, and the end stages of some cases of meningitis and encephalitis.

Traumatic causes of chronic dementia include anoxia, diffuse axonal injury (following a severe blow to the head), and dementia pugilistica ("punch drunk"), which results from repeated concussive trauma. A chronic subdural hematoma may present with a dementia-like syndrome.

Dementia, often in association with hostility and severe mood disorders can result from repeated sub-clinical head trauma or "mild concussions" over an extended period. Called chronic traumatic encephalopathy (CTE) , the condition is only confirmed after death via brain autopsy. [12, 13] Athletes involved in a variety of contact sports, most notably football and soccer (heading the ball), are at increased risk for CTE. [14] This is true even in the absence of any severe blows to the head. CTE has been diagnosed in young athletes playing contact sports for a relatively short period and dying of other causes (allowing for brain autopsy). This has led to reconsideration of the safety of football and soccer in children and teenagers. 

Toxins causing chronic organic brain syndrome include heavy metals (eg, lead in solder, ceramic glazes), organic chemical exposures, severe carbon monoxide poisoning, and chronic substance abuse.

Deficiencies of vitamin B-12 and folate can cause organic brain syndrome.

Autoimmune causes include systemic lupus erythematosus, giant cell arteritis, and sarcoidosis. Delirium has been associated with treatment or withdrawal of treatment of autoimmune diseases with high-dose steroids.

Psychiatric illnesses mimicking dementia include the pseudodementia of major depression in elderly persons and chronic schizophrenia (originally termed "dementia praecox"). Mania and hypomania as seen in bipolar disorder can be confused with delirium. In its severe form, “excited delirium” can be exacerbated by physical restraining and can lead to sudden cardiac death.

Other causes to consider include chronic endocrinopathies, Wilson disease (copper storage disease), and lipid storage diseases.

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