Multiple Sclerosis Cognitive Scale (MSCS): A brief psychometrically robust metric of patient-reported cognitive difficulty.

Background: Existing metrics of patient-reported cognitive difficulties in multiple sclerosis (MS) are lengthy, lack psychometric rigor, and/or fail to query prevalent expressive language deficits.

Objective: Develop a brief psychometrically robust metric of patient-reported cognitive deficits that includes language items; the Multiple Sclerosis Cognitive Scale (MSCS).

Method: Exploratory factor analysis (EFA) was conducted on 20 Perceived Deficits Questionnaire (PDQ) items plus five newly developed language questions in a large MS sample and matched respondents without neurologic disease. Independent confirmatory principal components analysis (PCA) assessed EFA factor structure. Reliability of the new scale and subscales, and relationships with objective cognitive impairment and cognitive change, were assessed.

Results: EFA in patients (n = 502) and controls (n = 350), item analyses, and confirmatory PCA in an independent sample (n = 361 patients; 150 controls) supported construction of an eight-item scale with four two-item subscales: Executive/Speed, Working Memory, Expressive Language, and Episodic Memory. Internal consistency and test-retest reliability were excellent for the total MSCS (α = 0.93, ICC = 0.95) and good for each subscale (α's:0.83-0.87; ICCs: 0.86-0.92). MSCS showed medium-size links to cross-sectional objective cognitive impairment (η² = .06) and cognitive change over time (η² = .07); the traditional PDQ did not (η²s = 0.01 and 0.02).

Conclusion: The brief MSCS is a psychometrically robust, reliable, and valid metric of patient-reported cognitive deficits in MS that holds promise for improving assessment of MS cognitive dysfunction.