The cognitive burden of stroke emerges even with an intact NIH Stroke Scale Score: a cohort study

Background We aim to facilitate recognition of the cognitive burden of stroke by describing the parallels between cognitive deficits and the National Institutes of Health Stroke Scale (NIHSS), a widely used measure of stroke severity. Methods A consecutive cohort of 223 working-age patients with an acute first-ever ischaemic stroke was assessed neuropsychologically within the first weeks after stroke and at a 6-months follow-up visit and compared with 50 healthy demographic controls. The NIHSS was administered at the time of hospital admittance and upon discharge from the acute care unit. The associations between total NIHSS scores and domain-specific cognitive deficits were analysed correlatively and with a binary logistic regression. Results Of the NIHSS measurements (admittance median=3, range 0-24; discharge median=1, range 0-13), the total score at the time of discharge had systematically stronger correlations with cognitive impairment. Adjusted for demographics, the NIHSS discharge score stably predicted every cognitive deficit with ORs ranging from 1.4 (95% CI 1.2 to 1.6) for episodic memory to 1.9 (95% CI 1.5 to 2.3) for motor skills. The specificities of the models ranged from 89.5-97.7%, but the sensitivities were as low as 11.6-47.9%. Cognitive deficits were found in 41% of patients with intact NIHSS scores and in all patients with NIHSS scores 4, a finding that could not be accounted for by confounding factors. Conclusions Cognitive deficits were common even in patients with the lowest NIHSS scores. Thus, low NIHSS scores are not effective indicators of good cognitive outcomes after stroke.