6 - Cognitive Impairment Including Dementia
6.1About cognitive impairment and dementia
Cognitive impairment, also called cognitive dysfunction or neuropsychological impairment, refers to any impairment of a cognitive function such as:
- problem solving, or
Cognitive impairment may have any number of causes including:
- brain trauma
- anoxia (lack of oxygen to the brain)
- toxicities, or
- degenerative, metabolic or nutritional diseases*
(*Persistent cognitive impairment in association with other medical conditions is referenced in the following chapters: Cardiovascular Diseases and Disorders, Cerebrovascular Disease, Intracranial Tumours, Psychotropic Drugs, Neurological Disorders, Psychiatric Disorders, Chronic Renal Disease, Respiratory Diseases, Sleep Disorders, Traumatic Brain Injury and Vestibular Disorders)
The presentation of cognitive impairment is variable depending on the cognitive functions affected and the degree of impairment. Cognitive impairment may progress to dementia, it may remain stable, or there may be a recovery of normal cognitive function.
Dementia refers to a disorder characterized by memory impairment in conjunction with one or more other cognitive deficits. In North America, the most commonly used criteria for the diagnosis of a dementia are those articulated by the American Psychiatric Association. The defining features of dementia are:
- The development of multiple cognitive deficits that include both
- memory impairment (impaired ability to learn new information or to recall previously learned information), and
- one or more of the following cognitive disturbances:
- aphasia (language disturbance)
- apraxia (impaired ability to carry out motor activities despite intact motor function)
- agnosia (failure to recognize or identify objects despite intact sensory function), and
B. The cognitive deficits in criteria A (1) and (2) each cause significant impairment in social or occupational functioning and represent a significant decline from a previous level of functioning.
C. The deficits do not occur exclusively during the course of a delirium.
D. The deficits are not better accounted for by another Axis I disorder* (e.g. Major Depressive Episode, Schizophrenia)
(*This refers to the classification of psychiatric disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). See Chapter 14, Psychiatric Disorders, for more information on this classification system.)
Dementia has many causes and more than 100 types of dementia have been documented. The five most common types of dementia are:
- Alzheimer’s disease
- vascular dementia (multi-infarct dementia)
- mixed Alzheimer’s and vascular dementia
- dementia with Lewy bodies (Lewy body dementia), and
- frontotemporal dementia (Pick’s disease or Pick’s complex). Frontotemporal dementia may not meet all of the criteria noted for dementia, especially in the early stages, but may still result in significant functional impairment.
These types of dementia are all progressive and irreversible, and are characterized by impairments in multiple cognitive functions.
In Alzheimer’s disease, the most common form of dementia, the earliest cognitive symptoms include difficulties in:
- recent memory
- word finding
- confrontation naming
- orientation, and
Characteristics of later stages include:
- slowed rates of information processing
- attentional deficits
- disturbances in executive functions, and
- impairments in language, perception and praxis.
Less commonly, dementias can result from:
- head injury and trauma
- brain tumours
- hydrocephalus (excessive accumulation of cerebrospinal fluid (CFS) in the brain)
- bacterial and viral infections
- toxic, endocrine and metabolic causes, or
Some of these dementias may be reversible. Specific examples of reversible causes of dementia include:
- thyroid deficiency or excess
- vitamin B12 deficiency
- chronic alcoholism
- abnormal calcium levels
- dementia associated with celiac disease, and
- intracranial space-occupying lesions.
Treatment for dementia has become available over the last decade with cognition enhancing drugs such as donepezil (AriceptTM), galantamine (ReminylTM) and rivastigmine (ExelonTM). These drugs seem to improve symptoms of the disease in some stages of dementia but their therapeutic effect is variable. It is generally considered not likely that treatment with medication would improve cognition to a degree that would enable driving in those whose driving skills had declined to an unsafe level or those who had previously failed a driving assessment due to cognitive impairment.
Mild cognitive impairment
Mild cognitive impairment (MCI) is a term that usually refers to the transitional state between the cognitive changes associated with normal aging and the fully developed clinical features of dementia. The diagnostic criteria for MCI are evolving but in general it describes a cognitive decline that presents no significant functional impairment.
A simple summary of factors in determining degree of Dementia and Mild Cognitive Impairment include:
Mild cognitive Impairment (MCI)(Some memory impairment but dementia not definitively diagnosed)
|Mild Dementia||Moderate Dementia||Severe Dementia|
Forgets name, location of objects
May have trouble finding words
May have difficulty traveling to new locations
May have difficulty with problems at work
|Has difficulty with complex tasks or instrumental activities of daily living (eg finances, shopping, planning dinner, cooking, taking medication, telephoning etc.)||
Has difficulty with basics activities of daily living (eg eating, dressing hygiene)
Needs help choosing and putting on clothing
Requires prompting and assistance when bathing
Decreased ability to use toilet and is incontinent
Loses ability to walk and sit
Unable to smile
Delirium is a condition characterized by a disturbance of consciousness and a change in cognition that occurs over a relatively short period of time, usually hours to days.
Common causes of delirium include:
- vascular disorders (e.g. stroke, myocardial infarct)
- infections (e.g. urinary tract, chest)
- drugs (e.g. analgesics, sedatives, alcohol, illicit drugs), and
- metabolic disorders (e.g. renal failure, hepatic failure, endocrine disorders).
Although the symptoms of delirium may be similar to dementia, delirium is temporary and therefore considered a transient impairment for licensing purposes.
Estimates from the Canadian Study on Health and Aging (1991) suggest that 8% of all Canadians aged 65 and older meet the criteria for dementia, increasing to 34.5% for those 85 and older. A 2004 study projected that, in 2007, there would be 65,780 individuals with dementia in British Columbia, 44,130 of whom would have Alzheimer’s disease.
In relation to cognitive impairment from any cause that has not been diagnosed as dementia, research indicates that the prevalence is 8% in individuals aged 65 to 74, increasing to 42% for those 85 and older.
The prevalence of both cognitive impairment (all causes – not dementia) and dementia increases with age. As shown in the table below, when combined, the prevalence of cognitive impairment and dementia is 12% in those 65 to 74 and more than 72% in those 85 and older.
8 Source: Canadian Study of Health and Aging, 1991
6.3Cognitive impairment, dementia and adverse driving outcomes
Research clearly indicates that, as a group, those with dementia are at higher risk for adverse driving outcomes. In particular, individuals with dementia who experience behavioural disturbances and who are treated with psychotropic medications (e.g. antipsychotics, antidepressants) may be at increased risk. It is important to note that studies also indicate that many individuals with dementia show no evidence of deterioration of driving skills in the early stages of their illness.
The significance of cognitive impairment and dementia in relation to other medical conditions was highlighted in a 1999 study done in Utah. This study compared citations, crashes and at-fault crashes for individuals with medical conditions to those for healthy controls matched for age, gender and county of residence. As shown in the graph below, the results indicated that individuals with cognitive impairment (including dementia) had at-fault crash rates that were more than 3 times higher than controls. In comparison, the at-fault crash rate for those who had a history of alcohol or other drug abuse was 2 times higher than controls.
(9 Source: Diller, E, Cook, L, Leonard, D, Reading, J, Dean, JM, Vernon, D. Evaluating drivers licensed with medical conditions in Utah, 1992-1996. DOT HS 809 023. Washington, DC: National Highway Traffic Safety Administration.)
6.4Effect on functional ability to drive
|Condition||Type of driving impairment and assessment approach||Primary functional ability affected||Assessment tools|
|Persistent impairment: Functional assessment||Cognitive||
Cognitive impairment or dementia may affect one or more of the cognitive functions required for driving.
Drivers with cognitive impairment or dementia are not able to compensate for their functional impairment.
6.6Guidelines for Assessment
Eligible for any class licence if
|Conditions for maintaining licence||No conditions required|
|Information from health care providers||
|National Standard||Ineligible for any class of licence|
|Conditions for maintaining licence||Details of diagnosis|
|Information from health care providers||N/A|
|Rationale||A diagnosis of severe dementia indicates cognitive function is impaired to a degree that is unsafe for driving|