Dementia Diagnosis

Proper differential diagnosis between the types of dementia (cortical and subcortical - see below) will require, at the least, referral to a specialist, e.g., a geriatric internist, geriatric psychiatrist, neurologist, neuropsychologist or geropsychologist. However, there exist some brief tests (5–15 minutes) that have reasonable reliability and can be used in the office or other setting to screen cognitive status for deficits that are considered pathological. Examples of such tests include the abbreviated mental test score (AMTS), the mini mental state examination (MMSE), Modified Mini-Mental State Examination (3MS), the Cognitive Abilities Screening Instrument (CASI), and the clock drawing test.

An AMTS score of less than six (out of a possible score of ten) and an MMSE score under 24 (out of a possible score of 30) suggests a need for further evaluation. Scores must be interpreted in the context of the person's educational and other background, and the particular circumstances; for example, a person highly depressed or in great pain will not be expected to do well on many tests of mental ability.

Mini-mental state examination

The U.S. Preventive Services Task Force (USPSTF) reviewed tests for cognitive impairment and concluded:

MMSE

sensitivity 71% to 92%

specificity 56% to 96%

Modified Mini-Mental State examination (3MS)

A copy of the 3MS is online. A meta-analysis concluded that the Modified Mini-Mental State (3MS) examination has:

sensitivity 83% to 93.5%

specificity 85% to 90%

Abbreviated mental test score

A meta-analysis concluded: including the clock-drawing test. Although some may emerge as better alternatives to the MMSE, presently the MMSE is the best studied. However, access to the MMSE is now limited by enforcement of its copyright.

Another approach to screening for dementia is to ask an informant (relative or other supporter) to fill out a questionnaire about the person's everyday cognitive functioning. Informant questionnaires provide complementary information to brief cognitive tests. Probably the best known questionnaire of this sort is the Informant Questionnaire on Cognitive Decline in the Elderly.

The General Practitioner Assessment Of Cognition combines both, a patient assessment and an informant interview. It was specifically designed for the use in the primary care setting and is also available as web-based test. It can be accessed on www.gpcog.com.au.

Further evaluation includes retesting at another date, and administration of other (and sometimes more complex) tests of mental function, such as formal neuropsychological testing.

Laboratory tests

Routine blood tests are also usually performed to rule out treatable causes. These tests include vitamin B12, folic acid, thyroid-stimulating hormone (TSH), C-reactive protein, full blood count, electrolytes, calcium, renal function, and liver enzymes. Abnormalities may suggest vitamin deficiency, infection or other problems that commonly cause confusion or disorientation in the elderly. The problem is complicated by the fact that these cause confusion more often in persons who have early dementia, so that "reversal" of such problems may ultimately only be temporary.

Testing for alcohol and other known dementia-inducing drugs may be indicated.

Imaging

A CT scan or magnetic resonance imaging (MRI scan) is commonly performed, although these modalities do not have optimal sensitivity for the diffuse metabolic changes associated with dementia in a patient that shows no gross neurological problems (such as paralysis or weakness) on neurological exam. CT or MRI may suggest normal pressure hydrocephalus, a potentially reversible cause of dementia, and can yield information relevant to other types of dementia, such as infarction (stroke) that would point at a vascular type of dementia.

The functional neuroimaging modalities of SPECT and PET are more useful in assessing long-standing cognitive dysfunction, since they have shown similar ability to diagnose dementia as a clinical exam. The ability of SPECT to differentiate the vascular cause from the Alzheimer disease cause of dementias, appears to be superior to differentiation by clinical exam.

Recent research has established the value of PET imaging using carbon-11 Pittsburgh Compound B as a contrast medium (PIB-PET) in predictive diagnosis of various kinds of dementia, in particular Alzheimer's disease. Studies from Australia have found PIB-PET to be 86% accurate in predicting which patients with mild cognitive impairment would develop Alzheimer's disease within two years. In another study, carried out using 66 patients seen at the University of Michigan, PET studies using either PIB or another contrast agent, carbon-11 dihydrotetrabenazine (DTBZ), led to more accurate diagnosis for more than one-fourth of patients with mild cognitive impairment or mild dementia.