Differentiating between irreversible dementia and dementia that results from a medical condition involves a process of systematic elimination. Doctors often start by looking for conditions that are most readily correctable. If these possibilities can be eliminated, then more serious, irreversible dementiassuch as Alzheimer's diseaseare considered.
The presence of reversible disorders can complicate the diagnosis of irreversible forms of dementia. In these instances, diagnosing and treating the concurrent condition can provide a clearer view of any problems that persist.
The first step in diagnosis is a thorough medical history and physical examination to identify any vision, hearing, cardiovascular, thyroid, or other disorders. Although checking for these conditions might seem unnecessary, they often go unrecognized in older adults and can have a significant effect on memory.
For example, heart failure (a decrease in the heart's ability to pump blood) may impede mental functioning by reducing the amount of blood circulating to the brain. Recovering from cardiac arrest or heart bypass surgery also can affect memory. Research suggests that about 50% of people who undergo heart bypass surgery experience a decline in cognitive function.
The cognitive problems were believed to be related to the heart-lung machine used during the surgery. However, several studies have found that a newer type of heart bypass surgery called "off-pump" bypass (which does not require the heart-lung machine) did not reduce the risk of adverse cognitive changes.
Mental status tests, such as the Mini-Mental State Examination, the Short Test of Mental Status, or the Cognitive Capacity Screening Examination, are given to check for any general cognitive impairment. The Clock Drawing Test and the Time and Change Test are two other simple tests for dementia. All of these tests take just five to 15 minutes to complete and can serve as a baseline for comparison should further testing be necessary.
The medical history should include an interview with a family member or close friend. This type of interview can be crucial because someone close to the patient knows the individual's previous level of functioning and can help the physician determine whether cognitive deterioration has occurred.
The American Academy of Neurology recommends the following tests in the routine evaluation of a patient with suspected dementia:
- complete blood cell count
- electrolyte levels in the blood (potassium, sodium, and chloride)
- blood levels of glucose (sugar), urea nitrogen, and creatinine
- blood levels of vitamin B12
- liver function tests and thyroid function tests
- depression screening
A routine evaluation would not include single-photon emission computed tomography (SPECT), genetic screening, or testing for a variant form of the apolipoprotein E (APOE) gene that significantly increases the risk of developing Alzheimer's disease. Testing for syphilis or performing a lumbar puncture to check the spinal fluid for biochemical "red flags" (markers) of Alzheimer's disease would only be done in special circumstances.
The American Academy of Neurology maintains that the usefulness of positron emission tomography (PET), genetic markers for Alzheimer's disease (other than APOE), and biochemical markers for Alzheimer's disease in cerebrospinal fluid is not known at this time.