Duhaime's Law Dictionary

Dementia Definition:

A chronic impairment of cognitive and intellectual functioning including memory impairment, which interferes with the activities of daily living.

Related Terms: Insanity, Lunacy law, Mental Disorder, M'Naghten Rules, Incompetency, Incapacitated, Mentally Ill, Alzheimer's, Global Deterioration Scale, Folstein MMSE, ADEPT - Advanced Dementia Prognostic Tool

Tennenhouse writes:

"Dementia is any condition involving loss of mental function. mental function includes memory, judgment, concentration, reasoning power, ability to recognize relatives and friends, orientation as to time and place, ability to dress and feed one's self and other abilities to function normally.

"People of all ages, not just the elderly, may be affected."

Begley and Jeffreys wrote:

"A diagnosis of clinical dementia requires a finding that cognitive defects are severe enough to cause significant impairment in social or occupational functioning."

Stedman's Dictionary defines dementia as follows:

"The loss, usually progressive, of cognitive and intellectual functions, without impairment of perception or consciousness; caused by a variety of disorders including severe infections and toxins but most commonly associated with structural brain disease. Characterized by disorientation, impaired memory, judgment and intellect...."

The 17th edition of the Merck Manual uses these words:

"A chronic deterioration of intellectual function and other cognitive skills severe enough to interfere with the ability to perform activities of daily living."

Distinguished although similar to delirium. Generally, delirium develops rapidly while dementia usually develops gradually. Delirium may be reversed; dementia, once set in, rarely is. Further, delirium can require emergency medical attention whereas those that suffer from dementia do not generally require emergency treatment although the dementia can evolve to the point where the person requires extensive medical care.

Dementia typically emerges in stages for which psychiatry has developed a test (MMSE) and a scale (Global Deterioration Scale). A rough scale is presented by Tennenhouse as follows:

"MILD: work and social activities are impaired but the patient can continue to live independently.

"MODERATE: living independently is difficult and potentially dangerous.

"SEVERE: continuous supervision is necessary."

However, this scale should be used with caution. Dementia is properly scaled into seven groups and not three - see, for example, the Global Deterioration Scale.

Common causes of dementia include:

  • Alzheimer's disease;
  • Brain injury or tumor;
  • Hypothyroidism;
  • Severe alcohol or drug abuse;
  • Multiple sclerosis; and
  • Parkinson's disease.


  • Beers, Mark and Berkow, Robert, editors, The Merck Manual of Diagnosis and Therapy, 17th Ed. (Whitehouse Station, New Jersey: Merck Research Laboratories, 1999), page 1393.
  • Begley, Thomas and Jeffreys, Jo-Anne, Representing the Elderly Client Law and Practice (New York: Wolters Kluwer, 2010) §204 (page 2-66)
  • Duhaime, Lloyd, Duhaime's Legal Dictionary
  • Duhaime, Lloyd, Duhaime's Legal Citations & Abbreviations
  • Pugh, Maureen, (ed.), Stedman's Medical Dictionary, 27th Ed. (Baltimore: Lippincott Williams & Wilkins, 2000), page 470
  • Schmidt, J.E., Attorney's Dictionary of Medicine, Volume 2 (Newark, New Jersey: LexisNexis, 2009), page D-50
  • Tennenhouse, Dan, Attorney's Medical Deskbook, 4th Ed. (Minnesota: Thomson-West, 2006), §25:14

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