Doctors diagnose the cause of dementia by asking questions about the person's medical history and doing a physical exam, a mental status exam, and lab and imaging tests.

Tests can help the doctor learn whether dementia is caused by a treatable condition. Even for those dementias that cannot be reversed, knowing the type of dementia a person has can help the doctor prescribe medicines or other treatments that may improve mood and behavior and help the family.

Medical history

During a medical history and physical exam, the doctor will ask the affected person and a close relative or partner about recent illnesses or other life events that could cause memory loss or other symptoms such as behavioral problems. The doctor may ask the person to bring in all medicines he or she takes. This can help the doctor determine whether the problem might be caused by the person being overmedicated or having a drug interaction.

Although a person may have more than one illness causing dementia, symptoms sometimes can distinguish one form from another. For example, early in the course of frontotemporal dementia people may display a lack of social awareness and develop obsessions with eating, neither of which occurs early in other dementias.

Mental status exam

A doctor or other health professional will conduct a mental status exam. This test usually involves such activities as having the person tell what day and year it is, repeat a series of words, draw a clock face, and count back from 100 by 7s.

Other tests have been developed to diagnose dementia. Doctors can use one such test, Addenbrooke's Cognitive Examination, to distinguish Alzheimer's disease from frontotemporal dementia. Orientation, attention, and memory are worse in Alzheimer's, while language skills and ability to name objects are worse in frontotemporal dementia.⁸

Lab tests

Numerous medical conditions can cause mental impairment. During a physical exam, the doctor will look for signs of other medical conditions and have lab tests done to find any treatable condition. Routine tests include:

• Thyroid hormone tests to check for an underactive thyroid.
• Vitamin B12 blood test to look for a vitamin deficiency.
• Complete blood count, or CBC, to look for infections.
• ALT or AST, blood tests that check liver function.
• Syphilis test to look for this disease.
• Chemistry screen to check the level of electrolytes in the blood and to check kidney function.
• Glucose test to check the level of sugar in the blood.

Other lab tests that may be done include:

• HIV testing to look for AIDS.
• Erythrocyte sedimentation rate, a blood test that looks for signs of inflammation in the body.
• Toxicology screen, which examines blood, urine, or hair to look for drugs that could be causing problems.
• Antinuclear antibodies, a blood test used to diagnose autoimmune diseases.
• Testing for heavy metals in the blood, such as a lead test.

Imaging tests