Diagnosis of Alzheimer's Disease

How is Alzheimer's disease diagnosed?

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.

The other conditions should be screened for are:

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 non contrast 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.