Are Multiple Cerebral Infarcts Synergistic?

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Abstract
Objective: The goal of this study was to characterize the cumulative effects of multiple strokes on cognition. Design: We conducted a prospective, longitudinal case study with neuropsychological, neurological, and radiological evaluations. Setting: Research was conducted at the Boston (Mass) Veterans Administration Medical Center, Neurology Service, on successive inpatient hospital admissions. Patient: We followed up a 66-year-old right-handed man with multiple subcortical lacunae during a 3.5-year period during which he suffered two additional cortical infarctions. Main Outcome Measures: Each evaluation included approximately 3 hours of neuropsychological testing spanning a range of cognitive domains (attention, language, memory, visuospatial functions, response inhibition, and mental flexibility), full neurological examination, and computed tomographic scan. Results: The patient's stepwise cognitive decline was characterized by unexpected exacerbation of "frontal" neurobehavioral features following the occurrence of two posterior cortical lesions. At initial evaluation, the computed tomographic scan showed bilateral subcortical lacunae in basal ganglia and periventricular white matter, and symptoms included dysarthria and perseveration. The second evaluation, following a left posterior parietal lesion, revealed a range of new frontal features, including impulsivity, pull-to-stimulus, and difficulty shifting set. Following a subsequent right occipital infarct, further frontal lobe impairments emerged: forced grasp reflex and incontinence. Conclusions: We hypothesize that the cumulative effects of infarcts were synergistic. That is, the posterior cortical infarcts elicited frontal features that would not be expected from a simple sum of these lesions' effects.