Alzheimer's Disease (cont.)
How is the diagnosis of Alzheimer's disease made?
As of June 2007, there is no specific "blood test" or imaging test that is
used for the diagnosis of Alzheimer's disease. Alzheimer's disease is diagnosed when:
1) a person has
sufficient cognitive decline to meet criteria for dementia; 2) the
clinical course is consistent with that of Alzheimer's disease; 3) no other brain
diseases or other processes are better explanations for the dementia.
What other conditions should be screened for?
There are many conditions that can cause dementia, to include the following:
Neurological disorders: Parkinson's disease,
cerebrovascular disease and
strokes,
brain tumors, blood clots, and multiple sclerosis can sometimes be
associated with dementia although many patients with these conditions are
cognitively normal.
Infectious diseases: Some brain infections such as
chronic syphilis,
chronic
HIV, or chronic fungal meningitis can cause dementia.
Side effects of medications: Many medicines can cause cognitive impairment,
especially in elderly patients. Perhaps the most frequent offenders are drugs
used to control bladder urgency and
incontinence. "Psychiatric medications" such
as anti-depressants and anti-anxiety medications and "neurological medications"
such as anti-seizure medications can also be associated with cognitive
impairment.
If a physician evaluates a person with cognitive impairment who is on one of
these medications, the medication is often gently tapered and/or discontinued to
determine whether it might be the cause of the cognitive impairment. If it is
clear that the cognitive impairment preceded the use of these medications, such
tapering may not be necessary. On the other hand, "psychiatric," "neurological,"
and "incontinence" medications are often appropriately prescribed to patients
with Alzheimer's disease. Such patients need to be followed carefully to determine whether these
medications cause any worsening of cognition.
Psychiatric disorders: In older persons, some forms of depression can cause
problems with memory and concentration that initially may be indistinguishable
from the early symptoms of Alzheimer's disease. Sometimes, these conditions, referred to as
pseudodementia, can be reversed. Studies have shown that persons with depression
and coexistent cognitive (thinking, memory) impairment are highly likely to have
an underlying dementia when followed for several years.
Substance Abuse: Abuse of legal and/or illegal drugs and
alcohol abuse is
often associated with cognitive impairment.
Metabolic Disorders: Thyroid dysfunction, some steroid disorders, and
nutritional deficiencies such as vitamin B12 deficiency or thiamine deficiency
are sometimes associated with cognitive impairment.
Trauma: Significant head injuries with brain contusions may cause dementia.
Blood clots around the outside of the brain (subdural hematomas) may also be
associated with dementia.
Toxic Factors: Long term consequences of acute carbon monoxide poisoning can lead to an encephalopathy
with dementia. In some rare cases, heavy metal
poisoning can be associated with dementia.
Tumors: Many primary and metastatic brain tumors can cause dementia. However,
many patients with brain tumors have no or little cognitive impairment
associated with the tumor.
The Importance of Comprehensive Clinical Evaluation
Because many other disorders can be confused with Alzheimer's disease, a comprehensive
clinical evaluation is essential in arriving at a correct diagnosis. Such an
assessment should include at least three major components; 1) a thorough
general medical workup, 2) a neurological examination including testing of
memory and other functions of thinking , and 3) a psychiatric evaluation to
assess mood, anxiety, and clarity of thought.
Such an evaluation takes time -
usually at least an hour. In the United States healthcare system,
neurologists,
psychiatrists, or
geriatricians frequently become involved. Nonetheless, any
physician may be able to perform a thorough evaluation.
The American Academy of Neurology has published guidelines that include
imaging of the brain in the initial evaluation of patients with dementia. These
studies are either a noncontrast CT scan or an
MRI scan. Other imaging
procedures that look at the function of the brain (functional neuroimaging),
such as SPECT, PET, and
fMRI, may be helpful in specific cases, but generally
are not needed. However, in many healthcare systems outside of the United
States, brain imaging as not a standard part of the assessment for possible
Alzheimer's disease.
Despite many attempts, identification of a blood test to diagnose Alzheimer's
disease has
remained elusive. As of June 2007, such testing is neither widely available nor
recommended.
Next: What is the prognosis of a person with Alzheimer's disease? »
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