Subjective sleepiness ratings (Epworth sleepiness scale) do not reflect the same parameter of sleepiness as objective sleepiness (maintenance of wakefulness test) in patients with narcolepsy.

OBJECTIVE: To evaluate whether subjective (Epworth Sleepiness Scale or ESS) and objective (Maintenance of Wakefulness Test or MWT) tests of sleepiness are equally useful in patients with narcolepsy.

METHODS: Correlational study evaluating the relationship between ESS and MWT as measures of sleepiness.

SETTING: Multi-center.

PATIENTS: 522 patients (17-68 year old men and women) with a current diagnosis of narcolepsy.

INTERVENTIONS: None.

RESULTS: Correlations were: MSLT and MWT, r = 0.52 (P<0.001); MWT and ESS, r = -0.29 (P<0.001); MSLT and ESS, r = -0.27 (P<0.001). Regression curve estimation using linear and curvilinear models revealed no difference among linear and curvilinear models between MWT and MSLT, and between MSLT and ESS. However, curvilinear models were better at explaining the relationship between MWT and ESS, with the cubic model being the best. As the level of severe sleepiness (as measured by the MWT) changed, the ESS remained stable.

CONCLUSIONS: In a large narcolepsy sample, the MWT and ESS are not equally useful, and do not measure the same parameter of sleepiness.