Cerebral Oxygen Metabolic Stress in Children and Adults With Large Vessel Vasculopathy Due to Sickle Cell Disease.

Background and objectives: Large vessel vasculopathy (LVV), or moyamoya syndrome, increases the risk of stroke in patients with sickle cell disease (SCD), yet effective treatments are lacking. In atherosclerotic carotid disease, previous studies demonstrated elevated oxygen extraction fraction (OEF) as a predictor of ipsilateral stroke. In a SCD cohort, we examined hemispheric hemodynamic and oxygen metabolic dysfunction as tissue-based biomarkers of cerebral ischemic risk in patients with LVV.

Methods: Children and adults with SCD were recruited from a SCD clinic associated with a tertiary medical center and underwent prospective brain MRI and MR angiography. LVV was defined as ≥75% stenosis in a major anterior circulation artery, excluding occlusion or previous revascularization surgery. Baseline characteristics, cerebral blood flow (CBF), normalized OEF (nOEF), infarct volume, white matter microstructure, and brain volume were compared in hemispheres with vs without LVV. In a cross-sectional analysis, mixed-effects linear multivariable models examined the effect of LVV on: (1) CBF and nOEF, as tissue markers of hemodynamic and oxygen metabolic stress, respectively, and (2) endpoints of cerebral ischemic injury including infarct volume, white matter microstructure, and brain volume.

Results: Of 155 patients (22 [12-31] years, 57% female), 33 (21%) had ≥25% stenosis, 22 (14%) had ≥50% stenosis, 14 (9%) had 75%-99% stenosis, and 5 (3%) had 100% occlusion. After excluding hemispheres with previous revascularization surgery, LVV was present in 16 hemispheres from 11 patients. Hemispheres with (N = 16) vs without (N = 283) LVV had lower CBF (25.2 vs 32.1 mL/100 g/min, p = 0.01) and higher nOEF (0.99 vs 0.95, p = 0.02). On multivariable analysis, CBF was nonsignificantly lower (β = -0.16, p = 0.07) while nOEF remained higher in hemispheres with LVV (β = 0.04, p = 0.03). Moreover, LVV was associated with greater hemispheric infarct volume, microstructural disruption, and atrophy.

Discussion: Beyond greater infarct burden, LVV was associated with hemispheric atrophy and white matter microstructural injury. As an indicator of active hypoxia, elevated nOEF likely represents a compensatory response to flow-limiting stenosis in hemispheres with LVV. The study is limited by a small number of patients with severe stenosis. Future studies are needed to evaluate the potential of tissue-based CBF and nOEF in assessing stroke risk and guide timely treatment of vasculopathy in SCD.