Multiple Sclerosis Cognitive Scale (MSCS): A Brief Psychometrically-Robust Metric of Patient-Reported Cognitive Difficulty

Background: Cognitive decline is common in multiple sclerosis (MS), but existing metrics of patient-reported cognitive difficulties are lengthy, lack psychometric rigor, and/or fail to query expressive language deficits prevalent in MS. Objective: To develop the Multiple Sclerosis Cognitive Scale (MSCS) as a brief psychometrically-robust metric of patient-reported cognitive deficits. Method: Exploratory factor analysis (EFA) was conducted on 20 items of the Perceived Deficits Questionnaire (PDQ) plus five newly developed language questions in a large sample of patients with MS and matched respondents without neurologic disease. Confirmatory principal components analysis (PCA) in an independent sample assessed the EFA factor structure. Reliability of the new scale and subscales was assessed, and we evaluated the relationship between the new scale and objective cognitive impairment. Results: EFA in patients (n=502) and controls (n=350), item analyses, and confirmatory PCA in an independent sample of patients (n=361) and controls (n=150) supported construction of an eight-item scale with four 2-item subscales assessing Executive / Speed, Working Memory, Expressive Language, and Episodic Memory. Internal consistency was excellent for the total MSCS (α=0.93) and good for each subscale (Executive / Speed, α=0.85; Working Memory, α=0.83, Expressive Language, α=0.87; Episodic Memory, α=0.85). There was a medium-sized relationship between objective cognitive impairment and MSCS scores (η2 [95%CI] = 0.06 [0.01, 0.13], but cognitive impairment was not related to the traditional PDQ (0.01 [0.00, 0.06]). Conclusion: The MSCS is supported as a brief, psychometrically-robust, reliable, and valid metric of patient-reported cognitive deficits in MS. The MSCS holds promise for improving assessment of MS cognitive dysfunction in clinical and research settings.