Dementia is a progressive deterioration of intellectual function due to the death of brain cells. Dementia can be caused by medical conditions such as hypothyroidism or stroke, drug toxicity or brain injury. Some conditions are treatable, and others cause irreversible brain damage. Alzheimer’s disease (AD) is irreversible, and in western countries, it accounts for more than half of dementia cases. Currently, the only way to diagnose AD definitively is through a brain autopsy. However, on living patients, physicians can correctly diagnose AD about 90 percent of the time based on mental and behavioral symptoms, a physical examination, and neuropsychological and laboratory tests.
A physician will normally take a history of mental and behavioral symptoms, using information provided by the patient and the family. In nearly 75 percent of cases, AD starts with the inability to remember recent events and to learn and retain new information. Early stage AD patients experience memory problems that interfere with daily living and steadily worsen. Other early AD symptoms can include difficulty managing money, driving, orientation, shopping, following instructions, abstract (conceptual) thinking and finding the right words. There may also be other problems, such as poor judgment, emotional instability and apathy. AD can be distinguished from other types of dementia in part by the symptoms exhibited, the extent to which these symptoms occur and the speed with which the disease progresses.
A physical examination will be performed to help identify and rule out other potential causes of dementia. This exam will normally include a general physical, blood tests and urinalysis. Through a blood test, for example, the physician can measure thyroid function; hypothyroidism or failure to produce sufficient thyroid hormones is common in the elderly and can cause dementia. Dementia may also be the result of a vitamin B12 deficiency which is common in the elderly, and can be measured through blood tests. Physicians may use brain scans (such as magnetic resonance imaging or MRI) to rule out other possible causes of dementia, including brain tumors, stroke, blood accumulation on the brain surface or other conditions. In addition, brain scans can show characteristic structural changes present in AD. Physicians may administer an electroencephalogram (EEG) to measure the electrical activity in the brain. Occasionally, spinal fluid may be tested through a lumbar puncture.
Neuropsychological tests identify behavioral and mental symptoms associated with brain injury or abnormal brain function. The neuropsychological tests used will depend on the symptoms and the dementia’s state of advancement. Usually, physicians start with a brief screening tool, such as the Mini-Mental Status Examination (MMSE), to help confirm that the patient is experiencing problems with intellectual functions. The MMSE includes tests of memory, attention, mathematical calculation and language. If a patient has severe dementia, further neuropsychological testing beyond the MMSE is usually not necessary. However, for patients with mild intellectual deficits, more tests may be needed to determine whether the patient is simply showing signs of advanced age or is developing AD. The patient may be referred to a neuropsychologist, who will administer a battery of tests to identify more specific deficits.