Section 22
Miscellaneous conditions that may affect fitness to drive


The fitness to drive of any patient must be assessed on an individual basis.

22.1 Overview

There are a number of medical conditions with the potential to influence driver fitness that have not been discussed in detail in previous sections of this guide. This section lists some of these conditions meriting special attention.

22.2 Obesity

Although most patients with obesity will be able to continue driving, morbid obesity may be incompatible with driving certain vehicles. For example, a professional truck or bus driver must perform certain tasks associated with the vehicle’s security that may involve clambering on or under the vehicle, tasks that a person with morbid obesity will be unable to accomplish.

Many patients with obesity report that they are unable to wear seat belts; however, most vehicles can accommodate seat belt extensions. For patients with severe obesity, it may be necessary to consider deactivating the airbags to avoid inadvertently deploying the airbag and thereby causing injury. Regardless of safety device use, motorists and occupants with morbid obesity remain at greater risk of death if involved in a motor vehicle crash (Joseph et al., 2017; Elkbuli et al., 2019).

Cardiovascular, respiratory, and metabolic comorbidities are common in patients with obesity. The presence of sarcopenic obesity, suggested by poor grip strength, slow gait, and history of immobility, should raise questions about fitness to drive. Hypoglycemia is common after a patient has undergone bariatric surgery (Lehmann et al., 2021).

22.3 Delirium

Delirium, a rapid-onset change in cognition, may be associated with many of the conditions reviewed elsewhere in this guide. Delirium can present with obvious symptoms, such as hallucinations, and altered level of consciousness, often of fluctuating degree. Delirium can also present with more subtle subsyndromal symptoms, such as poor concentration and slow mentation. As patients recover from the obvious symptoms of delirium, they may temporarily experience a phase of more subtle symptoms that could still affect their ability to resume driving. The hypoactive subtype of delirium is more common than the hyperactive type and is often overlooked.

For patients who have experienced an episode of in-hospital delirium, the treating physician should determine whether there are residual signs of cognitive impairment or specific signs of delirium at the time of discharge. If such signs exist, the physician should ask the patient not to drive until they have been re-evaluated by the family physician after a length of time judged by the discharging physician as adequate for recovery. It is important to communicate concerns about impairment and any relevant findings to the physician who will perform the follow-up assessment.

If the delirium is detected by the family physician, the patient should be advised not to drive until they have been seen in a follow-up appointment to determine whether there has been a response to treatment of the condition that triggered the delirium.

If the physician is uncertain regarding whether it is safe for the patient to resume driving, it is recommended that the physician extend the period during which the patient should not drive and then arrange to see the patient in follow-up. If follow-up evaluations do not demonstrate complete recovery, and concerns remain regarding fitness to drive, then referral to a driving assessment centre is appropriate. If the physician is concerned that the delirium has unmasked dementia or a mental health problem, then treatment and/or referral to the appropriate specialists is reasonable.

22.4 General debility

“General debility” describes a decline in the capacity to lead a normal life, caused by the person’s state of health. It is defined as the sequelae of multiple medical conditions and syndromes that produce the specific and general symptoms of pain, fatigue, cachexia, and physical disability, as well as cognitive symptoms of attention, concentration, memory, and developmental and/or learning deficits. An exhaustive list of the conditions causing general debility, both common and rare, exceeds the scope of this guide, but examples include eating disorders, hepatic encephalopathy (Nguyen et al., 2018; Formentin et al., 2019), kidney disease (Kepecs et al., 2018), rheumatoid arthritis, and chronic fatigue syndrome. It is important to assess the fitness to drive of patients with advanced disease (Weir et al., 2017; Mansur et al., 2018).

Medications used to combat the actual disease process, as well as its signs and symptoms, may also produce effects that contribute to the state of general debility (see Section 6, Drugs). With the expansion of both medical knowledge and medication therapies, this category becomes wider, and its relevance to the issue of safety in driving becomes more important.

22.5 Common conditions may merit special consideration

Driving is such an integral part of daily living in Canada that it is easy to forget that many patients, no matter how old they are, contract medical conditions that can influence their driving fitness yet continue to go about their daily activities (including driving) to the best of their abilities. In fact, many look upon the process of living their lives as normally as possible as a challenge. Even the most common conditions may affect these patients’ performance behind the wheel.

Consequently, it is important for physicians and allied health care professionals to include counselling on driving in their routine advice to such patients. This is especially true for chronic conditions such as diabetes mellitus, where continuing to live a relatively normal life is possible, so long as reasonable precautions are observed. Unfortunately, unless patients receive counselling on how to compensate for their condition, they may engage in behaviour that is incompatible with safe driving.

More generally, physicians are reminded that an evaluation of fitness to drive (in accordance with the principles discussed in Section 2, Functional assessment — emerging emphasis) is essential for any patient, regardless of age, who is manifesting difficulty in maintaining activities that were part of the daily routine before the medical condition arose. In this context, the physician should consider not only the standard activities of daily living, but also additional activities that the patient previously enjoyed and has abandoned because of the medical condition, such as model making, reading, embroidery, or knitting. Overall, a patient’s fitness to drive must be questioned when they are unable to work (Lalić, 2019) .

According to a recent meta-analysis (Scott et al., 2017), history of a fall in drivers aged 55 years or older is predictive of a risk of being involved in a future road incident. It has been estimated that older drivers who declared having experienced a fall (from 6 months to 3 years previously) had a 40% increased risk of being involved in a motor vehicle crash relative to those who did not report a fall. As such, the literature has established a link between history of a fall and the risk of future motor vehicle crashes, but the mechanism underlying this association is not completely understood.

Acknowledgement: Assistance with the literature search on the topic of falls and risk of motor vehicle crashes was provided by Michel Gaudet, Direction de la recherche en sécurité routière, Vice-présidence aux stratégies de marketing, de sécurité routière et d’expérience employé, Société de l’assurance automobile du Québec.


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