| Dementia due to… | Approximate percentage of all dementia cases | Prognosis/course | Onset | Gender difference |
|---|
| Alzheimer’s disease | 70% | Poor | Gradual, often after age 65; early onset is rare | Slightly more common among women than men |
| Vascular disease | 15% (often comorbid with Alzheimer’s type) | Cognitive loss may remain stable or worsen in a stepwise fashion. | Abrupt; earlier age of onset than Alzheimer’s | More common among men |
| Lewy bodies | 15% (can be comorbid with Alzheimer’s type) | Poor | Gradual; age of onset is between 50 and 85 | Slightly more common among men than women |
| HIV infection | Less than 10% | Poor unless treated with antiretroviral medication | Gradual; depends on age at which HIV infection is acquired | Estimates of sex ratios vary, depending in part on the sex difference in HIV prevalence and the availability of antiretroviral treatment at the time a study is undertaken |
| Parkinson’s disease | Less than 10%; often comorbid with Alzheimer’s type and/or vascular dementia; about 50% of patients with Parkinson’s disease develop dementia | Poor | Gradual; typical age of onset is in the 70s | More men than women develop Parkinson’s disease, and so men are more likely to develop this type of dementia |
| Huntington’s disease | Less than 10% | Poor | Gradual; onset usually occurs in the 40s or 50s. | No sex difference |
| Head trauma | Unknown | Depends on the specific nature of the trauma | Usually abrupt, after the head injury | Unknown, but most common among young men |
| Substance-induced | Unknown | Variable, depends on the specific substance and deficits | Gradual; in the 30s and beyond | Unknown |
| Note: Most cases of dementia are caused by Alzheimer’s disease. However, dementia in a given person can arise from more than one cause, and the percentages in the second column reflect these comorbidities; for this reason, the numbers add up to more than 100%. |