Hepatic encephalopathy and fitness to drive

Low-grade hepatic encephalopathy (HE) may impair fitness to drive. Driving deficits have not yet been characterized, and their relation to psychometric test results is unclear.

Fifty-one cirrhotic patients and 48 age-matched controls underwent real driving in a multiple sensor and camera-equipped car, laboratory and "in-car" computer psychometry, and driving instructor's assessment.

Ten cirrhotic patients had no hepatic encephalopathy (HE0); 27 and 14 patients suffered from minimal HE (mHE) and overt HE grade I (oHE), respectively. During real driving, mHE and oHE patients showed significantly more violations of in-lane keeping, reduced break use, prolonged reaction times, and diminished stress tolerance compared with control or cirrhotic HE0 patients. In a self-evaluation questionnaire, mHE and oHE, but not the HE0, patients strongly overestimated their driving abilities. According to the driving instructor's assessment, 75%, 48%, and 39% of the patients with HE0, mHE, and oHE, respectively, were fit to drive, compared with 87% in the control group. Driving deficits in oHE patients were largely due to cognitive defects and prolonged reaction times, whereas, in mHE patients, mistakes and attention deficits predominated. Computer psychometric test results worsened with HE severity and age, whereas real driving was age independent. In 25 out of 94 patients, discordant results for driving fitness were obtained (driving instructor's assessment vs computer psychometry); in mHE and oHE patients, the concordance rates were only 62% and 64%, respectively.

Despite significant driving deficits, HE patients overestimate their driving abilities. The presence of mHE does not necessarily predict driving unfitness, and computer-based testings cannot reliably predict driving fitness.