PET scan of the brain of a person with AD showing a loss of function in the temporal lobe
Alzheimer diagnosis usually determines the disease clinically from the patient history, collateral history from relatives, and clinical observations, based on the presence of characteristic neurological and neuropsychological features and the absence of alternative conditions.
Alzheimer diagnosis uses advanced medical imaging with computed tomography (CT) or magnetic resonance imaging (MRI), and with single photon emission computed tomography (SPECT) or positron emission tomography (PET) can be used to help exclude other cerebral pathology or subtypes of dementia.
PET scan of the brain of a
person with AD showing a loss of
function in the temporal lobe
Alzheimer diagnosis and assessment of intellectual functioning including memory testing can further characterize the state of the disease. Medical organisations have created diagnostic criteria to ease and standardise the diagnostic process for practicing physicians.
Sometimes the Alzheimer diagnosis can be confirmed or made at post-mortem when brain material is available and an be examined histologically.
Alzheimer Diagnostic Criteria
The National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (now known as the Alzheimer's Association) established the most commonly used diagnostic criteria for Alzheimer's disease.
These criteria require that the presence of cognitive impairment, and a suspected dementia syndrome, be confirmed by neuropsychological testing for a clinical diagnosis of possible or probable AD.
A histopathologic confirmation including a microscopic examination of brain tissue is required for a definitive diagnosis. Good statistical reliability and validity have been shown between the diagnostic criteria and definitive histopathological confirmation.
Eight cognitive domains are most commonly impaired in AD—memory, language, perceptual skills, attention, constructive abilities, orientation, problem solving and functional abilities.
These domains are equivalent to the NINCDS-ADRDA Alzheimer's Criteria as listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) published by the American Psychiatric Association.
Alzheimer Diagnosis Tools
Neuropsychological screening tests can help in the diagnosis of AD. In them patients have to copy drawings similar to the one shown in the picture, remember words, read or sum.
Neuropsychological tests such as the mini-mental state examination (MMSE), are widely used to evaluate the cognitive impairments needed for diagnosis. More comprehensive test arrays are necessary for high reliability of results, particularly in the earliest stages of the disease.
Neurological examination in early AD will usually provide normal results, except for obvious cognitive impairment, which may not differ from standard dementia. Further neurological examinations are crucial in the differential diagnosis of AD and other diseases.
Interviews with family members are also utilized in Alzheimer diagnosis and assessment of the disease. Caregivers can supply important information on the daily living abilities, as well as on the decrease, over time, of the person's mental function.
A caregiver's viewpoint is particularly important, since a person with AD is commonly unaware of his own deficits. Many times, families also have difficulties in the detection of initial dementia symptoms and may not communicate accurate information to a physician.
Supplemental testing provides extra information on some features of the disease or is used to rule out other diagnoses. Blood tests can identify other causes for dementia than AD causes which may, in rare cases, be reversible.
Psychological tests for depression are employed, since depression can either be concurrent with AD or be the cause of cognitive impairment.
When available as a diagnostic tool, SPECT and PET neuroimaging are used to confirm a diagnosis of Alzheimer's in conjunction with evaluations involving mental status examination. In a person already having dementia, SPECT appears to be superior in differentiating Alzheimer's disease from other possible causes,compared with the usual attempts employing mental testing and medical history analysis.
A new technique known as PiB PET has been developed for directlyand clearly imaging beta-amyloid deposits in vivo using a tracer that binds selectively to the Abeta deposits.
Another recent objective marker of the disease is the analysis of cerebrospinal fluid for amyloid beta or tau proteins. Both advances have led to the proposal of new diagnostic criteria. |
