The doctor will ask when memory problems started and how quickly they got worse. This information, together with the person's age, can point toward a likely diagnosis. For example, if the person is elderly and has had consistently worsening memory and other problems for several years, a doctor may suspect Alzheimer's disease. If symptoms got worse rapidly, then Creutzfeldt-Jakob disease may be a likely cause. If the person has had a history of high blood pressure, diabetes and vascular disease, a doctor may suspect stroke.
To diagnose dementia, a doctor looks to see if a person's memory gets progressively worse, along with at least one of the following:
Difficulty understanding or using language
The inability to perform a purposeful act or sequence of motor activities
The inability to recognize familiar objects or people
Difficulty doing such complex tasks as planning or organizing
Doctors test people by testing memory and attention. A commonly used tool to screen for dementia is the Mini Mental State Exam. It consists of 11 short assessments, such as asking the person what day and year it is or have the person count backward from 100 by sevens (100, 93, 86, etc.). If the person answers correctly, dementia is less likely.
Laboratory tests can narrow down the possible causes. Some tests include:
Magnetic resonance imaging (MRI) or computed tomography (CT) scans – These create pictures of structures inside the head (similar to the way X-rays create images of bones). The pictures can reveal brain tumors and stroke. If these tests do not show any major abnormalities, the diagnosis could be Alzheimer's disease.
Positron emission tomography (PET) scans – Increasingly, these scans are being used to detect Alzheimer's disease, and conditions that can turn into Alzheimer's disease. They are not yet widely available.
Blood tests – These are done to help judge overall health and also to determine if vitamin B12 deficiency or very low levels of thyroid hormone may be contributing to the decreased mental functioning.
Lumbar puncture (spinal tap) – This test is rarely needed to evaluate dementia. Occasionally, your doctor may want to be certain that fluid pressure around the brain is normal. Also laboratory testing on a sample of spinal fluid can make sure there is no infection. Researchers are studying proteins in the spinal fluid to see if certain patterns can detect specific causes of dementia, or can predict the outlook (prognosis).