A diagnosis of dementia requires a medical history; physical examination, including  neurological examination); and appropriate laboratory tests.

 Taking a thorough medical history involves gathering information about the onset, duration, and progression of symptoms; any possible risk factors for dementia, such as a family history of the disorder or other neurological disease; history of stroke; and alcohol or other drug (prescription or over-the-counter) use.

 The American Psychiatric Association has established two generally accepted criteria for the diagnosis of dementia: (1) erosion of recent and remote memory and (2) impairment of one or more of the following functions:

 Language

 misuse of words or inability to remember and use words correctly (i.e., aphasia)

 Motor activity

 unable to perform motor activities even though physical ability remains intact (i.e., apraxia)

 Recognition

 unable to recognize objects, even though sensory function is intact (i.e., agnosia)

 Executive function

 unable to plan, organize, think abstractly

 Symptoms often develop gradually and show a progressive deterioration in function.

 Differential Diagnosis

Delirium The physician must distinguish between delirium and dementia. Delirium is a transient, acute mental disturbance that manifests as disorganized thinking and a decreased ability to pay attention to the external world. Delirium is often caused by infectious disease, brain tumor, poisoning, drug or alcohol intoxication or withdrawal, seizures, head trauma, and metabolic disorders. It is important to treat underlying conditions promptly, as they may be life-threatening or progressive if left untreated. Symptoms of delirium include the following:

   •        Disorientation as to person, place, and time

   •        Memory impairment

   •        Rambling, irrelevant, incoherent speech

   •        Reduced level of consciousness

 Neuropsychological tests are administered to assess difficulties in attention span, perception, memory, problem solving, and social and language skills. Responses to these tests may provide diagnostic clues.

 Blood tests may be ordered if the history and physical examination indicates an infectious, metabolic, or toxic condition. The results help the physician rule out Alzheimer’s and help determine an effective treatment plan.

   •        B12, folate, thiamine levels (vitamin deficiency)

   •        Blood glucose (hypoglycemia)

   •        Complete blood count (anemia)

   •        Drug screen (drug toxicity)

   •        Electrolytes (hypercalcemia, hypermagnamesia, hypernatremia)

   •        Liver function (liver disease)

   •        Lumbar puncture (normal-pressure hydrocephalus, encephalitis, meningitis)

   •        Thyroid function (hypothyroidism)

   •        VDRLT (syphilis and HIV infection)

 An analysis of DNA in the blood sample may reveal the ApoE4 gene, which is found in about one-third of Alzheimer’s disease patients.

 Electroencephalography (EEG) traces brain wave activity. Some central nervous system disorders cause distinct changes in brain wave activity. Alzheimer’s disease generally reveals "slow" waves.

An EEG can help distinguish a severely depressed or delirious patient whose brain waves are normal from a patient with a degenerative neurological disease.

 Imaging tests (MRI scan or PET scan) can detect structural, or physical, changes in the brain caused by stroke, blood clots, tumors, head injury, or hydrocephalus.