Mechanisms of early aphasia recovery

Background: The course of recovery of aphasia after stroke is highly variable. Some patients, even with severe aphasia, recover rapidly over the first days after onset. The mechanism of this early recovery (and later recovery) is unclear. Plausible accounts include reperfusion of ischaemic tissue surrounding the stroke, and rapid reorganisation of structure/function relationships. Aims: Based on a recent study showing that the severity of word comprehension impairment in acute stroke patients is strongly correlated with the severity of hypoperfusion (low blood flow) in Wernicke's area, we hypothesised that early recovery of spoken word comprehension is due to reperfusion (restored blood flow) to Wernicke's area. Our objective was to evaluate this hypothesis using advanced magnetic resonance imaging techniques of perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI). Methods and procedures: A series of 100 patients with acute, left hemisphere ischaemic stroke were evaluated within 24 hours of onset or worsening of symptoms, and 3 days later, using PWI, DWI, and a battery of lexical tasks, including spoken word/picture verification. A subset of 18 patients with impaired spoken word comprehension at Day 1 were included in the study. Chi square analysis was used to identify the association between early recovery of spoken word comprehension and reperfusion of each of 10 Brodmann's areas (BA). Outcomes & results: Early recovery of spoken word comprehension was significantly associated with reperfusion of BA 22 (Wernicke's area), but not with reperfusion of other BAs. All patients who showed early recovery of word comprehension also showed reperfusion of Wernicke's area, due to carotid endarterectomy, carotid stenting, induced blood pressure elevation, or spontaneous reperfusion. Conclusions: Tissue recovery, brought about by restored blood pressure elevation, likely accounts for cases of rapid resolution of aphasia in the first few days of stroke. Other mechanisms of recovery, including reorganisation of structure/function relationships, and learning of compensatory strategies, are likely important in later stages of recovery.