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Minimal, covert, low-grade, or subclinical hepatic encephalopathy (HE) are labels that fail to capture the true clinical and social significance of this entity. Beyond liver outcomes, HE impairs quality of life, promotes falls and increases the risk of daily accidents at home, in the workplace, or when driving a car.
Recent surveys, however, from United States, Canada, Spain, and United Kingdom highlighted that criteria to define unfit drivers vary among countries and even between particular states without clear guidelines for the assessment of fitness to drive or the reporting of patients with HE.
Mitigation of these risks requires a wider perspective. This includes changes in public policy (including laws and regulatory actions from appropriate legal authorities about comorbidities associated with increased risk of traffic accidents) to education at multiple levels, organisational (including actions focused on patient organisations and social institutions), interpersonal (involving relatives, friends, and social networks) and individual (focused on improvement of skills, knowledge and attitudes of the patient to determine limitations when driving). Clinicians treating patients with cirrhosis play a central role in this plan beginning with the identification of risk factors. In the current issue of Journal of Hepatology, psychomotor vigilance task (PVT) appears useful in the detection of both conditions (unfitness to drive and HE) (see Fig. 1).
The impact of HE on driving: What the data says (and what it does not)
The fatigue and cognitive deficits that define covert HE, namely impaired attention, poor response inhibition, and delayed information processing, are highly consequential for driving performance. Indeed, covert HE is associated with both car crashes and suboptimal driving simulator performance.
Lauridsen et al. compared driving performance with official driving records. Patients with minimal HE by psychometric testing were more likely to be unsafe drivers (16%) than those with normal cognition (7%) and illegal turns in a simulator task were associated with actual car crashes.
Two studies have employed on-road driving tests, demonstrating that individuals with minimal HE overestimate their driving abilities, which are limited particularly with respect to passing, timely braking and steering wheel handling.
We therefore lack an efficient and accurate modality to assess fitness to drive among patients with cirrhosis at-risk of HE. This is not specific to HE, but rather a struggle seen in most chronic conditions that can impact driving.
The current study’s design
Seeking to bridge this gap, Formentin et al. enrolled 145 patients with cirrhosis (56% of whom had prior overt HE and 71% were on medical therapy for HE) who performed the PVT, all of whom were followed for an average of 13 ± 5 months and 117 of whom completed a questionnaire regarding their driving. The PVT is a test of the ability to maintain attention and is a widely used measure of vigilance and fitness to drive among patients with sleep disorders. It is a 10-minute assessment administered using a hand-held device. The PVT test-taker is asked to press a button in response to numerical stimuli and is evaluated in terms on the proportion of correct responses and their mean reaction time.
First, while the PVT had not been previously tested in patients with HE, among the 106 patients who competed neuropsychometric testing, the authors found consistent correlations between PVT performance and both psychometric HE scores and electroencephalography. Second, though driving performance was not assessed, the authors find that PVT performance was poorest among those who were not driving. Third, and most importantly, the authors found that PVT reaction times were associated with age- and model for end-stage liver disease-adjusted risk of HE-related hospitalisation and death at 6 and 12 months. The authors’ findings are strengthened by their relatively large sample size and the prediction of clinical events. However, as a test of driving fitness, additional research and external, prospective validation are needed. This is because most of the patients enrolled were actively treated for HE, most patients with HE were already not driving based on clinical criteria independent of PVT or minimal HE (MHE), and the authors did not exclude sleep apnoea, which can directly affect both driving and PVT performance. PVT changes were also not predictive of driving events in patients with or without MHE. Further, adverse outcome prediction using PVT indices is very promising but may not supersede a simple history of overt HE (yes/no) or other established measures of MHE, including those employed in this study
Driving requires an intricate coordination of neuro-cognitive domains with rapid responses to the vehicle within a changing environment. These faculties can be impacted by chronic diseases and especially alterations throughout the spectrum of HE. As the population ages and the prevalence of cirrhosis skyrockets, there is an important need to develop strategies that could stratify patients at high risk of driving impairment beyond current clinical practice.
While an ideal test would be a rapid point-of-care option that can exclude the majority of unsafe drivers, such a test is unlikely to appear given the relative rarity of traffic offenses. These have not been effective in gauging driving fitness in patients suspected of mild cognitive impairment and dementia, both much more prevalent conditions compared to HE or MHE.
The future lies in improving the comfort of patients, families and clinicians to recognise that driving history is an essential aspect of the holistic approach towards cirrhosis care. Until we as clinicians make driving issues a routine part of our patient evaluation, it is unlikely that any test or combinations thereof that assess driving would make a major difference in the daily function of our patients and their families.
The authors received no financial support to produce this manuscript.
Conflict of interest
Tapper (Advisory council: Salix, Consultant: Novartis, Research Grants to Institution: Valeant, Gilead), Bajaj (Research grants to institution: Valeant, Advisory Boards: Valeant, Grifols, Norgine), Romero-Gomez (invented of THDP-17, a glutaminase inhibitor for the treatment of HE, which was licensed by Janus Developments. Speaker fees: BAMA-GEVE, Merz, and Norgine).
Patients with hepatic encephalopathy (HE) exhibit psychomotor slowing and impairment of visuomotor coordination, inhibition and executive function, which can negatively impact on their fitness to drive. In 1995 Watanabe et al. found that 31% of patients with cirrhosis and 44% of patients with HE were unfit to drive based on their neuropsychological profiles.1 Bajaj et al. recently conducted a cost-effectiveness analysis to assess the benefits of different strategies of minimal HE diagnosis and treatment for reducing accident-related costs, concluding that diagnosis by the inhibitory control test (ICT) and subsequent treatment with lactulose was the most cost-effective approach, with a significant, potential reduction in societal costs by prevented accidents.