Dementia, Pseudodementia and Delirium: 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

Pseudodementia—Many elderly people fear that their memory and other mental abilities are diminishing as they grow older, even if this is not the case. Some may be anxious, depressed, or suffering from pseudodementia, a type of severe depression that occurs mostly in elderly people.

The cognitive changes that resemble dementia include slow motor movements and thinking and short-term memory loss. Patients who are depressed may be apathetic and answer questions without attempting to provide the correct response. They may exhibit poor eye contact and little spontaneous movement.

Laboratory Tests

Depending on the patient's medical history and neurological examination, one or more diagnostic tests may be performed to identify the underlying cause of dementia.

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.

For example, a patient with Alzheimer's disease is usually cooperative, attentive, and gives appropriate responses, but will display memory loss. A patient with hydrocephalus is usually distracted and less cooperative.

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)

Huntington's disease is diagnosed by analyzing DNA in the blood sample and counting the number of times the genetic code for the mutated HD gene is repeated. Individuals diagnosed with HD usually have 40 or more such "repeats"; those without it, 28 or fewer.

Similarly, 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 (CT scan, MRI scan, PET scan) can detect structural, or physical, changes in the brain caused by stroke, blood clots, tumors, head injury, or hydrocephalus. A CT scan can show the characteristic structural changes that occur with Huntington's disease.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 01 Jan 2000

Last Modified: 10 Sep 2015