Unusual or strange behavior involves actions that are not typical of that individual. This may include chronic, progressive loss of memory, or loss of the ability to concentrate and perform other mental tasks.

There are many causes of unusual or strange behavior, including numerous medical and psychiatric illnesses. Two of the more common causes are delirium and dementia:

• Delirium is characterized by:
  • Sudden decreased level of consciousness
  • Association with medical illness, particularly high fever
• Dementia is characterized by:
  • Chronic, progressive loss of cognitive function
  • Association with brain disorders

Possible causes in older people include:

• Malnutrition (particularly vitamin B12 and thiamine deficiency)
• Medications
• Alcohol in excess
• Chronic exposure to cold (hypothermia)
• Emotional problems (depression or feeling useless)
• Head injury (subdural hematoma)
• Unfamiliar surroundings
• Dehydration
• Electrolyte abnormality
• Infection (including pneumonia, gastroenteritis, urinary tract infection)
• Thyroid disorders (either underactive or overactive)
• Alzheimer's disease

• Anxiety, emotional problems
• Side effects of medication for attention deficit disorder, such as Ritalin
• Side effects of antidepressants, such as Prozac
• Illicit drug use (particularly stimulants such as amphetamines and cocaine)
• Diseases affecting the nervous system (neurological diseases)
• Non-neurological diseases, particularly with fever (for example, pneumonia)
• Low or high thyroid function
• Environmental hazards

For dementia or delirium that appears to be caused by a brain tumor, head injury, stroke, infection, fever, or pneumonia, seek immediate medical attention.

For delirium caused by anxiety and emotional problems, reassurance and loving support are recommended. Frequent feedback about time, place, and names of people providing care can be helpful.

For delirium or dementia caused by malnutrition, a proper diet and vitamin supplements are recommended after medical evaluation.

For delirium caused by medication, consult your doctor about adjusting dosage, changing medications, or discontinuing them.

For delirium or dementia caused by alcohol in excess, complete abstinence is required.

For delirium related to illicit drug use, stop taking the offending substance.

For delirium caused by emotional problems, psychological counseling is recommended.

For delirium caused by hypothermia, adequate heat and warmth is required. Re-warming should be carefully monitored.

Delirium that follows surgery is usually temporary, but avoid prolonged use of sedatives and pain killers.

For dementia caused by Alzheimer's disease, there is no prevention, but possible new treatments should be discussed with the doctor. Sympathetic care, occupational therapy, and family support are needed.

For dementia caused by Huntington's chorea, provide supportive care.

For delirium resulting from environmental causes, make a concerted effort to modify the environment or change environments.

For delirium caused by low thyroid function, see your health care provider about thyroid hormone replacement treatment.

Contact your regular health care provider or a neurologist if:

• Dementia or delirium is present
• Unusual or strange behavior is severe, prolonged, unexplained, or is impairing lifestyle

The health care provider will perform a physical examination and will obtain the patient's medical history. The physical examination will probably include a detailed neurological evaluation.

Medical history questions documenting unusual or strange behavior in detail may include the following:

• What unusual behaviors are present?
• How much is the lifestyle affected?
• Can the person eat, dress, and perform other everyday activities?
• When did the unusual behavior begin?
• Is it getting worse, better, or staying about the same?
• How fast is the behavior changing?
• What other symptoms are present?

Diagnostic tests that may be performed include the following:

• CT scan of the head
• Other neurological tests
• Blood tests