Do Changes in Oxygen Metabolism in the Unaffected Cerebral Hemisphere Underlie Early Neurological Recovery After Stroke?

Abstract

Background and Purpose Whether an initial depression of function in the unaffected hemisphere (“transcallosal diaschisis”) plays a role in early neurological recovery after acute stroke remains controversial. Previous studies were confounded by lack of acute-stage assessment with follow-up and by the problem of defining a suitable control group, since preexisting stroke risk factors may influence prestroke cerebral metabolism. We evaluated with positron emission tomography (PET) the relationships between unaffected-hemisphere (ie, contralateral) oxygen consumption (cCMRO 2 ) and quantitative neurological assessments (and their respective evolution over time) after ischemic stroke. Methods Among 30 consecutive patients with first-ever middle cerebral artery ischemic stroke studied with the 15 O equilibrium method, we selected all survivors (n=19; mean age, 74.6 years) who were investigated both within the first 18 hours after stroke onset (PET 1 ; mean, 11±4 hours) and 15 to 30 days later (PET 2 ; mean, 24±10 days), with each patient serving as his/her own control. Neurological deficits were quantified using Orgogozo's middle cerebral artery scale (N score) at each PET session. Neurological changes were calculated as changes in the N score. A late CT scan coregistered with PET provided infarct topography and volume index. Results At PET 2 , we observed the overall expected neurological recovery. There was a nearly significant trend for a decrease in cCMRO 2 from PET 1 to PET 2 , especially for the neocortex ( P =.08, F test); in a subgroup of eight patients with large infarcts, this CMRO 2 decline was significant ( P <.05) in the mirror region to the infarct. There was no significant correlation (Spearman's tests) between acute-stage cCMRO 2 and same-day N scores or between changes in cCMRO 2 versus changes in N score from PET 1 to PET 2 (any region). There was a nearly significant trend for lower PET 2 cCMRO 2 in the subgroup of eight patients with large compared with small infarcts ( P =.06). Conclusions We found no evidence for an influence of cCMRO 2 on acute-stage neurological deficit or for a role of the unaffected hemisphere in early recovery after acute MCA ischemic stroke. The decline in unaffected-hemisphere metabolism from the acute to the subacute stage in the face of overall clinical recovery appears clinically irrelevant. The fact that the neocortical cCMRO 2 at PET 2 tended to be lower, and declined significantly from PET 1 to PET 2 in the mirror region in the subgroup of patients with large infarcts, suggests that this delayed effect represents transcallosal fiber degeneration.