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:

  • memory
  • attention
  • language
  • problem solving, or
  • judgment.

Cognitive impairment may have any number of causes including:

  • brain trauma
  • anoxia (lack of oxygen to the brain)
  • infection
  • 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

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:

  1. The development of multiple cognitive deficits that include both
    1. memory impairment (impaired ability to learn new information or to recall previously learned information), and
    2. one or more of the following cognitive disturbances:
      1. aphasia (language disturbance)
      2. apraxia (impaired ability to carry out motor activities despite intact motor function)
      3. 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
  • concentration.

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
  • depression
  • hydrocephalus (excessive accumulation of cerebrospinal fluid (CFS) in the brain)
  • bacterial and viral infections
  • toxic, endocrine and metabolic causes, or
  • anoxia.

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

Vocabulary limited

Loses ability to walk and sit

Unable to smile

Delirium

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.

6.2Prevalence

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.

prevalence of dementia and cognitive impairment

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.

risk at fault crash: selected medical reasons

(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

Cognitive impairment

Dementia

Persistent impairment: Functional assessment Cognitive

Medical assessments

Functional Assessment

Cognitive impairment or dementia may affect one or more of the cognitive functions required for driving.

6.5Compensation

Drivers with cognitive impairment or dementia are not able to compensate for their functional impairment.

6.6Guidelines for Assessment

6.6.1 Cognitive impairment or dementia

National Standard

Eligible for any class licence if

  • Complete medical assessment indicates cognitive functions necessary for driving are not impaired, or
  • where required, functional driving assessment shows condition does not affect ability to drive
  • Conditions for maintaining a licence are met
BC Guidelines
  • If the treating physician identifies cognitive impairment, or dementia that may impair the cognitive functions necessary for driving, RoadSafetyBC may request a driving assessment, unless;
    • there has been no significant change in the individual’s condition or cognitive ability since a previous functional assessment
  • If cognitive screening indicates that the cognitive functions are significantly impaired, AND there is a diagnosis of cognitive impairment or dementia, OR there is compelling collateral information that indicates a safety risk, RoadSafetyBC will not generally request further assessments and the licence will be canceled  unless;
    • the entirety of the file information supports a finding of sufficient cognitive function to drive safely such that an opportunity for a driving assessment may be offered,  or;
    • the treating physician indicates cognitive screening  tests in fail range is related to other factors (e.g.  level of education, language),  RoadSafetyBC  may provide an opportunity for a driving assessmentent
  • If the individual has been diagnosed with severe dementia; RoadSafetyBC will not generally request further information, and the licence will be cancelled. Please see 6.6.2
Conditions for maintaining licence No conditions required
Reassessment
  • RoadSafetyBC will typically re-assess annually if an individual has
    • dementia, or
    • a cognitive impairment that is progressive
  • Otherwise, routine commercial or age-related re-assessment
Information from health care providers
  • Nature or cause of the cognitive impairment
  • Opinion of treating physician whether the cognitive impairment is progressive
  • Various tools such as OT driving assessments, cognitive screens and road tests may be helpful in assessing whether an individual with cognitive impairment is eligible to hold licence
Rationale
  • Functional assessment is required to determine if individual can drive safely
  • The results of cognitive screening tests such as the MOCA, MMSE, Trails B, Global Deterioration Scale, and/or others, while considering the entirety of the file information, will inform whether further assessment is required

6.6.2 Severe dementia

National Standard Ineligible for any class of licence
BC  Guidelines
  • RoadSafetyBC will not generally request further information; and the licence will be cancelled.
  • Drivers are not typically eligible for a licence if the driver has:
    • Been diagnosed with advanced or severe dementia
 
Conditions for maintaining licence Details of diagnosis
Reassessment N/A
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