Medical Conditions and Driving: A Review of the Literature (1960  2000)
TRD Page
Section1: Introduction
Section 2: Vision
Section 3: Hearing
Section 4: Cardiovascular
Section 5: Cerebrovascular
Section 6: Peripheral Vascular
Section 7: Nervous System
Section 8: Respiratory
Section 9: Metabolic
Section 10: Renal
Section 11: Musculoskeletal
Section 12: Psychiatric
Section 13: Drugs
Section 14: Aging Driver
Section 15: Anesthesia and Surgery
Appendix A
List of Tables
List of Figures
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Section 7:
Diseases of the Nervous System

7.3 Sleep Disorders

Sleep disorders are thought to be responsible for many motor vehicle crashes. However, it is difficult to establish reliable estimates of the contribution of sleepiness to motor vehicle crashes. The difficulty in identifying the role of sleepiness in crashes is due to the multifactorial nature of many crashes, and the lack of objective and reliable measures for assessing driver sleepiness (Pack, Pack, Rodgman, Cucchiara, Dinges, and Schwab, 1995). According to recent estimates, one to three percent of all highway crashes are caused by driver sleepiness (Knipling and Wang, 1994; 1995; Wang, Knipling, and Goodman, 1996; Webb, 1995). Narcolepsy and obstructive sleep apnea are two of the most common medical disorders that cause excessive daytime sleepiness, with obstructive sleep apnea the most common of the two disorders (Arbus, Tiberge, Serres, and Rouge, 1991; National Commission on Sleep Disorders Research Report, 1993). Both are believed to be associated with an increased risk of motor vehicle crashes. Literature relevant to both of these conditions is reviewed below.

7.3a. Narcolepsy

Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy, hallucinations, and sleep paralysis. Nocturnal polysomnograms and a Multiple Sleep Latency Test (MSLT) are used to confirm the diagnosis of narcolepsy. Current estimates suggest that 0.03 percent to 0.16 percent of the general population is affected, with men and women affected equally (Aldrich, 1990; Lyznicki, Doege, Davis, and Williams, 1998). The condition usually starts in adolescence or early adulthood. Treatment of narcolepsy includes the use of stimulants (methylphenidate HCl [Ritalin] or dextroamphetamine) for sleepiness and tricyclic antidepressants for cataplexy and sleep paralysis (Green and Stillman, 1998).

Excessive daytime sleepiness, which can affect driving performance, is generally believed to be the most debilitating of the symptoms (Green and Stillman, 1998). Cataplexy, a sudden episode of muscle weakness triggered by emotions (e.g., laughing, anger, surprise), also may affect driving performance. More than one quarter of all narcoleptics may suffer from cataplexy (Broughton, Ghanme, Hisikawa, Sugita, Nevismalova,and Roth, 1981).

Narcolepsy and Driving Literature Review

Despite the potentially negative impact narcolepsy may have on driving performance, there are few studies investigating the relationship between narcolepsy and driving performance (see Table 17). Aldrich (1989) compared self-reports of crashes from individuals with narcolepsy to those of controls. Results of that investigation revealed that patients with narcolepsy have higher self-reported rates of crashes due to sleepiness than controls. Self-reported crashes were 11 times greater in females with narcolepsy compared to controls and seven times greater in males with narcolepsy compared to controls.

Findley, Unverzagt, Suratt, Gabrizio, Guchyu, and Buckner (1991) compared the performance of nine individuals with narcolepsy with an age- and sex-matched control group on a computer program simulating long and monotonous driving (Steer Clear). The outcome measure was number of obstacles hit during a 30 minute testing session. Results revealed that the subjects with narcolepsy hit more obstacles (6.4 percent ± 3.2 percent) than the control group (0.8 percent ± 0.5 percent). Comparisons also were made between level of performance on Steer Clear and state recorded crash rates for a five-year period for individuals with narcolepsy and obstructive sleep apnea. The results revealed significantly higher crash rates in subjects with poorer performance on Steer Clear. The study, however, has a number of limitations. First, the sample size is small. Second, cut-off criteria for performance categories (normal, poor, and very poor performance) are not specified. Finally, it is unclear from the data the percentages of narcoleptic subjects and sleep apnea subjects exhibiting normal performance, poor performance, and very poor performance.

George, Boudreau, and Smiley (1996) investigated the performance of narcoleptics and controls on a divided attention driving test (DADT) involving tracking and visual search. Individuals with narcolepsy made significantly more tracking errors than controls. The differences between the two groups on the visual search test were less disparate. The pattern of findings suggests that individuals with narcolepsy have greater difficulty dividing attention compared to controls. However, baseline measures while performing each of the tasks separately were not available for either the narcoleptic group or the control group. Thus, the cost of performing both tasks together for each of the groups, and the possibility of cost differences between the two groups cannot be determined. Unknown also is the relationship between performance on laboratory based tests, such as the DADT, and on-road performance. Research exploring the relationship between the two is needed.

Table 17  Summary of Studies Examining the Relationship between Crashes and Narcolepsy and Simulator Performance and Narcolepsy





Aldrich et al. (1989)

Narc = 56
C = 70

a. Crashes anytime in lifetime.

b. Crashes due to sleepiness.

a) Males:
         76 percent (Narc) at least one
         crash versus 79 percent (C).

      48 percent (Narc) at least one       crash versus 74 percent (C).

b) Males:
         52 percent (Narc)
         versus 11 percent (C).

     74 percent (Narc)
     versus 6 percent (C).

George et al. (1996)

Narc = 16
C = 21

a. Tracking Errors.

b. Visual Search.
     i) Correct responses

     ii) RT (secs).

a) Narc = 196 (± 146) versus 71
                    (± 32) (C).

b) i. Narc = 35.3 (± 6.2) versus
                       38.4 (± 2.5)(C).

ii. Narc = 3.3 (± 1.1) versus
                    2.9 (± 0.8) (C).

Findley et al. (1991)

Narc = 9
C = 9

Steer Clear
-obstacles hit

Narc = 6.4 percent ± 3.2 percent. C = 0.8 percent ± 0.5 percent.


= Narcolepsy
= Controls
= Divided Attention Driving Test

Despite the paucity of research in this area, most medical associations and driving agencies (Canadian Medical Association, 2000; The British Columbia Medical Association, 1997; Canadian Council of Motor Transportation Administrators, 1994) recommend that an individual who suffers from attacks of narcolepsy should not be allowed to drive. The Canadian Medical Association (2000) specifically recommends that individuals with a diagnosis of narcolepsy supported by a sleep study and with uncontrolled episodes of cataplexy during the past 12 months (with or without treatment) not drive any type of motor vehicle. It also is recommended that those with a diagnosis of narcolepsy supported by a sleep study and with uncontrollable daytime sleep attacks or sleep paralysis during the past 12 months (with or without treatment) not drive any type of motor vehicle.