Evaluation of psychometric properties of patient-reported outcome measures frequently used in narcolepsy randomized controlled trials: a systematic review

Study objectives
To systematically determine subjective and objective outcome measures used to measure efficacy of narcolepsy interventions in randomized controlled trials (RCTs) in adults and children and assess psychometric properties of patient-reported outcome measures (PROMs) used.

Methods
We searched bibliographical databases and clinical trial registries for narcolepsy RCTs and extracted objective and subjective outcome measures. If PROMs were used, we searched for psychometric studies conducted in a narcolepsy population using bibliographical databases and appraised using Consensus-based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines.

Results
80 different outcome measures were used across 100 RCTs. Epworth Sleepiness Scale (ESS) (n=49) and Maintenance of Wakefulness Test (n=47) were the most frequently used outcome measures. We found nineteen validation studies of ten PROMs in narcolepsy populations. There was limited evidence for validity or responsiveness of the ESS; yet sufficient reliability (pooled ICC: 0.81–0.87). Narcolepsy Severity Scale (NSS) had sufficient reliability (pooled ICC: 0.71–0.92) and both adult and pediatric versions had sufficient discriminant validity (treated/untreated). Content validity was only evaluated in pediatric populations for ESS-CHAD and NSS-P and rated inconclusive. Quality of evidence of the psychometric studies for all scales ranged from very low to low.

Conclusions
Although recognized by regulatory bodies and widely used as primary outcome measures in trials, there is surprisingly little evidence for validity, reliability and responsiveness of PROMs frequently used to assess treatment efficacy in narcolepsy. The field needs to establish patient-centred minimal clinically important difference for the PROMs used in these trials.