Cognitive impairment in isolated subtentorial stroke

Background - Recent case reports have implicated subtentorial lesions of the brainstem or cerebellum as part of the neurocognitive circuitry. Aim - To determine whether cognitive impairment is part of the neurological deficit in isolated brainstem (IBSS) or cerebellar stroke (ICS), using bedside screening and formal neurocognitive assessment of higher cortical function. Methods - Accrual occurred through a hospital based stroke registry. Cognitive bedside tests and neuropsychological tests were employed for the detection of higher cortical function. Scores from each test were converted to age and education based z-scores. Scores at or below -1.5 SD were clinically defined 'impaired'. Scores were averaged across tests in each functional area. Results - Of the stroke patients (n = 1360), the infarct was isolated within the brainstem (IBSS) in (45 of 120 or 38%) and isolated within the cerebellum (ICI) in (37 of 79 or 46.8%). Comparison of the IBSS patients with cognitive impairment in one or more domains to those with brainstem (24 of 45 or 53%) and hemispheric cerebral infarcts: (43 of 72 or 58%) (Pearson Chi Square) was not significantly different (P = 0.49). The admission Canadian Neurological Score (mean 10.2, 95% CI: 9.7-10.2) and Rankin score at 1 month (mean 1.7, 95% CI: 2.1-1.4). Comparison of the number of ICI patients with cognitive impairment in one or more domains (13 of 37 or 35.1%) to those with cerebellar and hemispheric cerebral infarcts who had abnormal cognitive testing in one or more domains (16 of 36 or 44.4%) (Pearson Chi Square) was not significantly different (P = 0.41). The mean admission Canadian Neurological Scores for the ICI cases was 10.9 (95% CI: 10.5-11.2) on average. Their mean admission Rankin score was 1.7 (95% CI: 1.4-2.1). Neuropsychological testing for frontal/executive skills, immediate and delayed memory, and visuospatial abilities (n = 15), revealed that frontal abilities were most impacted by the isolated strokes in these patients (average frontal impairment index = -1.29 +/- 0.79) followed by delayed recall of verbal and visual information (mean = -1.18 +/- 1.17). Immediate memory (-0.51 +/- 0.75) and visuoconstructive skills (-0.06 +/- 0.88) were relatively spared. Overall, 47% of the patients showed impairment on frontal tasks while 40% had significant impairment in delayed recall. In contrast, only 13% had scores below the cutoff for immediate memory and none fell below the cutoff for visuoconstructive skills. Conclusion - Cognitive impairment is a common sequel of isolated subtentorial stroke. The frequency of impairment is similar either because of isolated brainstem or isolated cerebellar infarct, and similar to cognitive impairment with cerebral hemispheric lesions. Frontal networks or metacognition is the most frequently involved domain.