title: The cog-4 subset of the national institutes of health stroke scale as a measure of cognition: relationship with baseline factors and functional outcome after stroke using data from the virtual international stroke trials archive.
abstract: Background. Assessing poststroke cognitive impairment is complex. A subscale of the NIHSS, the Cog-4, has been proposed as a quick test of "cognitive impairment." but a study of its properties in a larger dataset is lacking. Methods. Data from 9,147 patients with acute stroke from the VISTA archive was used to generate Cog-4 scores. The statistical properties of Cog-4, its relationship with baseline clinical characteristics, and other functional outcome measures at day 90 were assessed. Results. Mean age of patients was 69.2 years and 45.8%, were females. Day-90 Cog-4 was highly positively skewed (skewness 0.926). Patients with left hemispheric stroke had higher day-90 Cog-4 score (P < 0.001). Age, stroke severity, and previous stroke were significant predictors of Cog-4. Cog-4 was significantly correlated with dependency (modified Rankin Scale, r s = 0.512), and disability (Barthel Index, r s = -0.493). Conclusions. The Cog-4 scale at day 90 cannot be considered a useful test of cognition since it only superficially measures cognition. It is heavily dependent on the side of stroke, is inevitably associated with functional outcome (being a subset of the NIHSS), and suffers from a profound "floor" effect. Specific and validated measures are more appropriate for the assessment of poststroke cognition than Cog-4.
authors.affiliation: Stroke Trials Unit, Division of Stroke, University of Nottingham, City Hospital Campus, Nottingham NG5 1PB, UK.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Ankolekar
authors.forename: Cheryl
authors.initials: C
authors.lastname: Renton
authors.forename: Nikola
authors.initials: N
authors.lastname: Sprigg
authors.forename: Philip M W
authors.initials: PM
authors.lastname: Bath