Dementia is a progressive deterioration of memory and other cognitive functions. Although extremely rare in people younger than sixty years old, dementia becomes increasingly more common with age. The incidence is about 10 percent at age sixty-five and doubles every ten years thereafter. The leading cause of dementia is Alzheimer's disease; other causes include cerebrovascular disease, Lewy-body disease, Parkinson's disease, alcoholism, HIV, and rare degenerative brain disorders, such as Pick's disease, progressive supranuclear palsy, Creutzfeldt-Jakob disease, and Hunt-ington's disease.
In addition to advancing age, factors that increase the risk of developing dementia are a family history of Alzheimer's disease, possession of the e4 ApoE allele (a genetic variant that increases the risk of Alzheimer's disease), traumatic brain injury, and exposure to toxic substances. Some new research suggests a causal role for certain types of viral infections, including herpes simplex virus type 1 and chlamydia, but these findings remain highly controversial.
Although people in the earliest stages of dementia often sense that something is wrong, the illness eventually robs them of the insight needed to appreciate their problem. Consequently, it's usually up to a family member or friend to recognize the symptoms. If you suspect that someone you know has dementia, arrange for a medical evaluation.
Doctors diagnose dementia by examining a person's behavior and cognitive function, as well as by gathering evidence from brain imaging studies and other laboratory tests, as I discussed in Chapter 6. The workup will consider possible reversible forms of dementia—for example, normal pressure hydrocephalus, which can be treated surgically, or chronic vitamin B12 deficiency, which 128, can be managed with regular injections of the vitamin.
Though some forms of dementia are reversible, many aren't. There are several medications for memory dysfunction associated with dementia that can bring about temporary, mild improvements and delay symptom progression. I discuss these medications in Chapter 8.
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