Driving impairment develops and worsens as Alzheimer's Disease (AD) progresses. It would be useful in the office setting to be able to predict which AD patients should not be driving. Typical cognitive disturbances seen in AD that might effect driving performance includes: visuospatial skills, visual attention abilities, judgment, planning skills, and the ability to perform complex tasks. Previous studies correlating on-the-road driving performance with cognitive measures have shown that the ability to do visual search tasks and visual tracking tasks, correlate best with driving performance. Most other standard neuropsychological tests have not correlated well. A diagnosis of mild AD by itself has also not been an adequate predictor of driving abilities. Unfortunately, most of those tasks that have shown good predictive value, require specialized equipment, special forms, or are burdensome to grade and administer in an office setting.
We investigated easy to administer measures of visual attention, visuospatial abilities, and executive function, in the office setting, to predict on-the-road driving performance in individuals with mild AD.
Prospective investigation of 18 consecutively referred subjects with mild probable AD who were still driving. This was a cross-sectional and limited longitudinal study with correlation analysis. A few patients were re-tested after one year for a total of 21 evaluations.
Patients were given the following tests:
- A standardized open road driving evaluation which was scored independently by a driving instructor blinded to the study design and cognitive test results
- Neruopsychological tests (pen and paper cognitive tests)
- 4-Turn test
Patients were scored on a 4 point scale (independent without difficulty=4, required cues=3, performed task with difficulty=2, unable to complete=1) for each of the following items:
- Transfer and preparation for driving
- Starting car; recognition and use of controls
- Driving (no traffic) - 28 points total (4 points maximum for each subitem): follows directions, proper use of controls, adequate turns left/right, serpentine, startle stop, parking, maneuverability to left/right
- Driving (traffic) - 48 points total (4 points maximum for each subitem): follows directions, proper mirror use, proper use of turn signals, proper intersection checks, recognition of road signs, turns to left/right, proper lane choice, lane changes, ability to stay within lanes, merging, scanning of environment, safety judgment/defensive driving
The 4-Turn test does not require any specialized equipment or scoring forms.
- With clues the patient is walked through a course in the clinic having 4 turns (2 right turns and 2 left turns) and then told to walk the course by themselves. They are given instructions along the way such as "turn right here at the exit sign" and "next we will be turning left here past the restroom" .
- Count one point for each correct turn they make. If they start to turn the wrong way and then self correct without being reminded, this is also counted as correct.
- If their score is perfect (4 points), they pass the test
- If they miss any turn, then they fail the test
Of the 21 evaluations:
- Average MMSE = 22.6 (Range: 15-27)
- 3 Females, 18 Males
- 12 passed the on-the-road driving test
- 9 failed the on-the-road driving test
We found significant correlations between the total driving score and 4 of the cognitive tests:
- Time to complete nonverbal cancellation test
- Choice reaction time
- Block design
- 4-Turn test
The 4-Turn test was the only one of the above tests that could be easily admnistered and scored in the office setting without specialized equipment or special forms. We found that:
- 78% of those failing the behind-the-wheel driving test, failed the 4-Turn test (Sensitivity of 78%)
- 83% of those passing the behind-the-wheel driving test, passed the 4-Turn test (Specificity of 83%)
- In the mild AD population, measures of visual attention, visuospatial abilities, and executive function may differentiate individuals at risk for unsafe driving
- The 4-Turn test may be an appropriate means to help determine if a patient should continue driving
- The 4-Turn test can be easily administered in the office setting and does not require any specialized equipment or scoring forms
- The 4-Turn test predicts well those who should not drive as well as those who are still able to drive
- Before making any final recommendations regarding driving status, the practitioner must always take into account other factors including reports on direct observations of driving abilities, physical health, and any behavioral problems