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Diagnosing Alzheimer's Disease

Alzheimer's Disease is diagnosed by a physician, often a neurologist or psychiatrist, after taking a careful history, performing a thorough physical examination including a neurological examination, and doing the appropriate laboratory and imaging tests. The goal of this examination is firstly to assess whether the patient meets the diagnostic criteria for Alzheimer's Disease, and also to determine whether there may be any identifiable medical conditions that could explain the individual's symptoms, as this would go against a diagnosis of Alzheimer's Disease.

Medical conditions that can be mistaken for Alzheimer's Disease

Such conditions include vascular dementia, Parkinson's disease, Huntington's disease, brain tumors, subdural hematoma, normal-pressure hydrocephalus, HIV infection, neurosyphilis, hypothyroidism, deficiencies of Vitamin B12, folic acid, niacin or calcium, or any substance-induced conditions.

Biological tests to diagnose Alzheimer's Disease

For a long time, the only way to know for certain that someone had pure Alzheimer's Disease, and not a different form of dementia like Vascular or Mixed Dementia, was to do an autopsy to identify the presence of characteristic amyloid plaques and neurofibrillary tangles in the cerebral cortex. Obviously, this can only be done after the individual has already passed away.

However, more recently, it has been found that measuring the amyloid beta-42/tau ratio in the cerebrospinal fluid (CSF) can serve as an accurate biomarker of Alzheimer's Disease [ref], and can even be used to detect early forms of this disease [ref].

There is also a kind of brain imaging technique, called a PiB PET scan, which can detect amyloid plaques in the brain. Studies have shown that this scan can be useful for diagnosing Alzheimer's Disease and also detecting early forms of this condition [ref, ref, ref].

Rating scale for measuring dementia and cognitive impairments

The Folstein Mini Mental State Examination (MMSE) is a brief protocol of questions and tasks that a clinician administers to a patient in order to assess whether any cognitive impairments are present [ref]. Performance can be affected by one's education level and cultural background, and by the presence of conditions such as Depression or Delirium. This instrument remains very popular because of its ease of use and has become something of a standard for measuring the extent of an individual's cognitive impairments in clinical settings. A perfect score is 30. A score of 23 or below suggests a high likelihood that one suffers from dementia; 18-23 suggests mild dementia, 10-18 suggests moderate dementia, and less than 10 suggests severe dementia.

The Montreal Cognitive Assessment (MoCA) is another brief test that clinicians can administer, which better captures executive function deficits than the MMSE. A score below 26 suggests Mild Cognitive Impairment or Alzheimer's Disease [ref].

The Functional Assessment Staging (FAST) scale is a way of determining the stage of an individual's dementia based on the symptoms they display [ref]. A clinician simply notes the patient's symptoms and then refers to the FAST chart to determine the stage to which the symptoms correspond. Knowing at what stage the individual is in helps to assess the effectiveness of the treatment and to know what kind of assistance the individual requires.

The Clock-Drawing task is a simple test where one is asked to draw face of a clock with the numbers in proper position and with the hands indicating the time "10 past 11." Difficulties with this task are readily apparent and suggest that the individual may be suffering from some cognitive impairments.

The Alzheimer Disease Assessment Scale-Cognitive (ADAS-Cog) is a semistructured interview that is given by a clinician trained in using this scale. The interview takes about 30-45 minutes, and it assesses the level of an individual's cognitive impairments. It is used most commonly in research trials.


Symptoms & Definition