Pearls & Oy-sters: Driving Safety in Photosensitive Genetic Generalized Epilepsy

Discussion

Generalized spike-wave discharges can occur on EEG without a clinical accompaniment of absence seizures, the so-called “subclinical” discharges. Many studies have shown that with better clinical testing, transitory cognitive impairment, manifest most commonly as increased reaction time, accompanies these seemingly subclinical discharges.^1,-,4

In early experiments from the 1940s, the discharge bursts lasting 1–3 seconds had normal reaction times, and longer bursts showed impairment.¹ Nevertheless, some other studies showed an increase in reaction time even with short bursts lasting 0.5–1.5 seconds; however, there was no increase in errors of omission during such short bursts.³ Another study showed that the initial 3 seconds and the final 1.5 seconds were associated with less consciousness impairment than the intervening period.² All these studies were limited mainly by sample size (n = 1 to 8) and varying methods of testing consciousness. More recently, a pilot study of driving simulation in people with generalized spike-wave discharges showed correlation of lack of response to stimulation with the duration and amplitude of spike-wave discharges. This pilot study showed that generalized spike-wave discharges with no response to stimuli were significantly longer than those with appropriate responses (8.47 ± 3.10 vs 1.85 ± 0.69 seconds, p < 0.001).⁴ Again, the study had a low sample size of 9 although 88 bursts were studied. Although the data regarding this are limited, as discussed above, there is a suggestion of correlation of transitory cognitive impairment with duration of generalized spike-wave bursts.

Transitory cognitive impairment is of clinical importance, especially when it poses a risk for injury or death; the most common scenario is driving a motor vehicle. Hence testing for impairment of consciousness becomes important in a patient who has generalized spike-wave discharges without overt absences. The effect of duration of generalized spike-wave discharges on driving ability was shown in a recent study with high fidelity driving simulator; reaction times to stimulation correlated with the duration of generalized spike-wave bursts.⁴ We tested our patient with gross motor, fine motor, and a concentration task, as described above; we found no impairment in these tasks during the photoparoxysmal bursts. However, we did not record reaction times, and we aborted photic stimulation at ∼3 seconds. Longer duration bursts might have caused impairment if we did not abort the photic stimulation. For this reason, we tested the patient’s flashing light tolerance with polarized blue sunglasses on and could complete photic stimulation without the occurrence of any PPR.

About 5% of people with epilepsy have evidence of photosensitivity on EEG, and about a third of these have visually induced seizures.⁵ Certain environmental factors cause a flashing effect during driving; these include sunlight breaking up along a tree-lined road, acoustic barrier posts interrupting the sunlight, and noise barrier tunnels with a transparent roof.⁶ Various lenses have been tested that could effectively block the flashing light frequencies and prevent photosensitive seizures. The efficacy depends on lens color and transmittance.^8,-,10 Eighty-three patients were tested to suppress photosensitivity during intermittent photic stimulation by using different types of lenses. A type of lens named Z1 was found to be significantly more effective in blocking photosensitivity effectively, compared to the other lenses.¹⁰ Z1 is a blue lens of an ultraviolet material with an 80% luminance cut. Subsequently, a large multicenter study showed the disappearance of PPR with the use of Z1 lenses in 76%, and the response was considerably reduced in an additional 18%. PPR remained unchanged in only 6%.⁷ These lenses are commercially available in Italy. Due to the lack of availability of this particular lens type, we tested our patient with polarized blue sunglasses⁸; this aborted the PPR. We were able to advise the patient that she is safe to drive with the polarized blue sunglasses on.

Blue and polarized sunglasses (any commercially available ones) may have efficacy in curtailing photosensitivity in people with epilepsy; efficacy of these must be tested in the EEG laboratory in the setting of evaluation of ability to drive. Further studies are needed to evaluate whether the efficacy is consistent with repeat stimulations, especially in the setting of higher epileptogenicity such as sleep deprivation or antiseizure medication withdrawal.