Behavior - unusual or strange

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Central nervous system

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.

Acting strangely

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

Review Date: 11/15/2006
Reviewed By: Paul Ballas, D.O., Department of Psychiatry, Thomas Jefferson University Hospital, Philadelphia, PA. Review provided by VeriMed Healthcare Network.