Focusing on vigilance instead of sleepiness in the assessment of narcolepsy: high sensitivity of the Sustained Attention to Response Task (SART)

Abstract

Study objective: The severity of narcolepsy is commonly measured with the Multiple Sleep Latency Test (MSLT), focusing on the tendency to fall asleep. A neglected but perhaps equally important complaint is impaired performance in the waking state. We evaluated the Sustained Attention to Response Task (SART) for the quantification of vigilance in narcolepsy.

Design: The SART involves withholding key presses to 1 in 9 target stimuli. In the present study, it was administered prior to each of 5 MSLT sessions in a 1-day study. The Epworth Sleepiness Scale was administered to measure subjective sleepiness. SART and MSLT results (number of errors and sleep latency) were compared using Receiver Operator Curves, sensitivity, and specificity.

Setting: Tertiary narcolepsy referral center in a university hospital.

Patients: Fifteen untreated narcoleptics and 15 matched controls.

Interventions: None.

Measurements and results: The area under the receiver operating curve was 0.97 for the MSLT and 0.95 for the SART. Sensitivity and specificity for the MLST were 80% and 100% using a cutoff point of 5 minutes. For the SART, these values were 87% and 100%, using a 5-error cutoff. The SART and MSLT showed no correlation with each other or with the Epworth Sleepiness Scale.

Conclusions: The SART, measuring attention, was abnormal as often as the MSLT, measuring sleepiness. The inability to remain vigilant during the day may be the most serious complaint in narcolepsy, since it impairs performance. The SART is valid in this respect, is easy to administer, and takes little time.