Development of a patient reported outcome scale for fatigue in multiple sclerosis: The Neurological Fatigue Index (NFI-MS)

Abstract

BackgroundFatigue is a common and debilitating symptom in multiple sclerosis (MS). Best-practice guidelines suggest that health services should repeatedly assess fatigue in persons with MS. Several fatigue scales are available but concern has been expressed about their validity. The objective of this study was to examine the reliability and validity of a new scale for MS fatigue, the Neurological Fatigue Index (NFI-MS).MethodsQualitative analysis of 40 MS patient interviews had previously contributed to a coherent definition of fatigue, and a potential 52 item set representing the salient themes. A draft questionnaire was mailed out to 1223 people with MS, and the resulting data subjected to both factor and Rasch analysis.ResultsData from 635 (51.9% response) respondents were split randomly into an 'evaluation' and 'validation' sample. Exploratory factor analysis identified four potential subscales: 'physical', 'cognitive', 'relief by diurnal sleep or rest' and 'abnormal nocturnal sleep and sleepiness'. Rasch analysis led to further item reduction and the generation of a Summary scale comprising items from the Physical and Cognitive subscales. The scales were shown to fit Rasch model expectations, across both the evaluation and validation samples.ConclusionA simple 10-item Summary scale, together with scales measuring the physical and cognitive components of fatigue, were validated for MS fatigue.

Validation of the Brazilian version of the neurological fatigue index for multiple sclerosis

“…It has been recognized that for such an instrument to be clinically useful, it needs to be validated, appropriate for the disease in question, reliable and easy to interpret and filled out 25 . The NFI-MS/BR showed a good level of patient acceptability and required only a few minutes to complete, as seen in previous studies 5,13 . Acceptability is supported when the scores observed are also well distributed 20 .…”

“…The meticulous process used in this study was important for identifying potential problems with the instrument content. Through assuring these equivalences, it was expected to maintain the psychometric properties of the NFI-MS/BR as properly docu mented in prior studies 5,11,12,13 . It has been recognized that for such an instrument to be clinically useful, it needs to be validated, appropriate for the disease in question, reliable and easy to interpret and filled out 25 .…”

“…A summary NFI-MS score can be calculated containing 10 items from both domains (items 1 to 7 from physical subscale and items 9, 11, and 12 from cognitive subscale). Both sleep domains were only regarded as provisional in the original publication 5 .…”

“…Concerns regarding the quality of existing measurements led Mills et al 5 to develop the 'Neurological Fatigue Index for MS' (NFI-MS), with rigorous methodology that fulfills current scale development criteria and has the psychometric properties satisfying Rasch measurement model expectations. This instrument provides a potential guide for MS fatigue assessment that can be used in research and clinical practice 9,10,11,12 .…”

“…The Fatigue Severity Scale (FSS) 2 and Modified Fatigue Impact Scale (MFIS) 3 are the most widely used instruments for measuring MS fatigue, although limitations regarding their development and measurement properties have been reported. Moreover, they were not specifically developed for MS patients 4,5,6 . Studies using the Rasch measurement model have identified a need for certain items to be removed from the FSS [4] and MFIS [6] so that their measurements can be considered valid and reliable.…”