Unusual or strange behavior involves performing actions that are not normal for the person.

Unusual or strange behavior may include:

• Loss of memory that continues over time or gets worse
• Loss of the ability to concentrate and perform other mental tasks

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

• Delirium -- Sudden or quick onset of reduced consciousness, awareness, perception, or thought that may be a symptom of a medical illness such as brain or mental dysfunction
• Dementia -- Chronic, worsening loss of cognitive function that occurs with brain disorders

Possible causes of strange behavior in older people include:

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

Possible causes in people of all ages include:

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

A doctor should check any unusual behaviors or personality changes. Treatments are based on the following causes of delirium:

• Brain tumor, head injury, stroke, infection, fever, or pneumonia -- seek immediate medical attention
• Anxiety and emotional problems -- support, talk therapy, and medications
• Malnutrition -- medical exam, followed by proper diet and vitamin supplements
• Medication -- ask the doctor about adjusting the dosage, changing medications, or stopping them
• Excess alcohol -- stop drinking (abstinence)
• Illicit drug use -- stop taking the drug and seek a doctor's advice for withdrawal symptoms
• Emotional problems -- psychological counseling
• Hypothermia -- warmth (rewarming should be carefully monitored)
• Surgery -- this is usually temporary, but avoid long-term use of sedatives and painkillers
• Alzheimer's disease -- medications, sympathetic care, occupational therapy, family support
• Huntington's chorea -- supportive care
• Environmental causes -- change the environment or change environments
• Low thyroid function -- see your health care provider about thyroid hormone replacement treatment

Contact your regular health care provider or a doctor who treats disorders of the nervous system (neurologist) if:

• The unusual or strange behavior is severe, long-term, unexplained, or is affecting your life
• You have dementia or delirium

The health care provider will perform a physical examination and will take a medical history. The physical examination will probably include a detailed evaluation of the nervous system (neurological evaluation).

Medical history questions may include:

• 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?

The following tests may be performed:

• Blood tests
• CT scan of the head
• Mental status test
• Other neurological tests