Diagnosis of dementia is made after performing a physical examination and asking questions about the person's medical history. The physical examination includes a complete neurological examination and tests to check mental functions. This is termed mental status examination.

Apart from mental status examination generalised tests to detect other diseases conditions contributing to dementia are also prescribed. It is, however, difficult to confirm the diagnosis and its actual cause for all individuals especially in early stages.

Diagnosis and interviews with the physician for diagnosis is best if a family member accompanies the patient to help him or her remember better.

What does dementia diagnosis involve?

Diagnosis of dementia involves:

• Detailed evaluation of personal history including education and employment
• Detailed evaluation of history of other medical ailments and detailed history of any medication or drug of abuse that the individual is taking. Certain drugs may also be responsible for dementia-like features in a person.
• Assessment of mental abilities using a range of tests.
• Blood tests to rule out other causes such as Vitamin B12 deficiency.
• Imaging studies of the brain like CT scan and MRI scan to look at the structural damage if any in the brain

Assessment of mental abilities

There are several questionnaire based tests that help in assessing the mental abilities of the patient.

One widely used questionnaire is the Mini Mental State Examination (MMSE). The MMSE assesses long and short term memory, concentration, attention span, language and communication skills, and ability to plan ahead and to follow and understand a given set of instructions.

Each of the test parts has a score. The scores are usually a maximum of 30 points in total. For example for assessment of short term memory a list of items and objects are provided to the individual who is asked to repeat it back in a while. There are other items such as writing a short sentence that is grammatically correct or identifying the current day of the week, followed by the date, the month, the season and the year.

MMSE cannot diagnose dementia by itself but it is useful for assessing the level of mental impairment. A score above 25 is deemed normal, score of 18 to 24 indicates mild to moderate impairment and a score of 17 or below indicates serious mental impairment. These may be affected by education and employment and that should be taken into account.

What is assessment based on?

For assessment the following are individually evaluated:

• Attention and concentration ability
• Orientation to the present time and place and to the person they are with
• Memory both short- and long-term are evaluated
• Praxis is examined - this involves looking at whether they can get dressed, lay a table, etc.
• Language function as evaluated during questioning
• Executive function involving problem-solving abilities

Assessment for other underlying conditions

There are several blood tests that are used to rule out other conditions that may be responsible for the patient's symptoms. Tests commonly prescribed for this purpose include:

• Full blood tests – this helps in detecting conditions like anemia and infections.
• Blood glucose test – this helps in the diagnosis of diabetes.
• Urine analysis – this helps detecting kidney problems and diabetes.
• Blood ammonia levels, urea and creatinine levels and blood urea nitrogen values (BUN) are tested to evaluate kidney causes of confusion and dementia like symptoms.
• Measurement of thyroid hormones - a measurement of thyroid hormones may be taken in order to screen for thyroid disorders. This includes an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism).
• Measurement of vitamin B12 levels – a Vitamin B12 deficiency may be associated with declining mental faculties and thus this test is important.
• Blood levels of opioids, drugs of abuse or alcohol are important to diagnose other causes of dementia like features.
• Imaging scans – these are performed to check the brain for abnormalities. A CT scan or MRI scan can help detect brain lesions such as a brain tumor. Imaging scans can also identify changes in the appearance of the brain that may indicate dementia. Some of these include shrinkage to the outer layer of the brain, changes to the blood vessels, presence of blood clots that might have resulted in vascular dementia etc.
• Single photon-emission computed tomography – this is recommended if Alzheimer's disease, fronto-temporal dementia or vascular dementia is suspected. A SPECT scan is similar to a CT scan but can assess the blood flow within the brain. This can help differentiate between the three types of dementia.
• Electroencephalograph (EEG) to detect brain function abnormalities.
• Assessment for depressive disorders - depression may cause a “pseudo-dementia” and needs to be ruled out.
• CSF examination should be used if Creutzfeldt-Jakob disease or other forms of rapidly progressive dementia are suspected.
• Genetic analysis should be prescribed where an inherited cause is suspected.