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

Acting strangely

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 medical 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

Psychiatric illnesses that are often associated with unusual or strange behavior include:

• Anxiety disorder
• Bipolar disorder
• Depression
• Psychosis
• Schizophrenia

Possible causes of strange behavior in older people include:

• Alcohol consumption in excess
• Alzheimer's disease
• Chronic exposure to cold (hypothermia)
• Dehydration
• Hypoglycemia
• 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 (sleeping pills, pain relievers)
• Thyroid disorders (either underactive or overactive)
• Unfamiliar surroundings

Possible causes in people of all ages include:

• Diseases affecting the nervous system (neurological diseases)
• Recreational drugs (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 medications

A doctor should evaluate any unusual behaviors or personality changes. Treatments are based on the following causes of strange behavior:

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

Schedule an appointment with 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 your lifestyle affected?
• Can you 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 or MRI of the head
• Electroencephalogram (EEG)
• Mental status test
• Neuropsychological testing
• Urine tests

Inouye SK. Delirium and other mental status problems in the older patient. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 26.

Knopman DS. Alzheimer's disease and other dementias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 425.