The Neurological Sleep Index: A suite of new sleep scales for multiple sclerosis

OBJECTIVE: The objective of this study was to develop patient-reported outcome measures for sleep dysfunction and sleepiness in multiple sclerosis (MS), since there are currently no MS-specific measurement tools for these clinically important entities. METHODS: Items were generated from semi-structured interviews followed by cognitive debrief. A 42-item pool was administered to patients with MS at three neuroscience centres in the UK. Comparator scales were co-administered. Constructs were validated by Rasch analysis, guided by initial exploratory factor analysis. RESULTS: There were two supraordinate qualitative themes of diurnal sleepiness and non-restorative nocturnal sleep. Rasch analysis on 722 records produced three scales, which corresponded to diurnal sleepiness, non-restorative nocturnal sleep and fragmented nocturnal sleep. All had excellent fit parameters, were unidimensional and were free from differential item functioning. A summed raw score cut-point of 31/48 in the Diurnal Sleepiness Scale equated to the standard cut-point of 10 on the Epworth Sleepiness Scale (ESS). CONCLUSION: Three high-quality measurement scales were developed, and together they compose the Neurological Sleep Index for MS (NSI-MS). The Diurnal Sleepiness Scale might provide an alternative to the ESS. The Non-Restorative Nocturnal Sleep Scale and the Fragmented Nocturnal Sleep Scale appear to be the only such measures for use in MS.