Blood-brain barrier integrity and brain entropy in reversible cerebral vasoconstriction syndrome

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Abstract
Elucidating functional brain dynamics under different blood-brain barrier (BBB) permeabilities may resolve the enigmatic pathophysiology of reversible cerebral vasoconstriction (RCVS); however, relevant investigations are lacking. We aimed determine the relationship between brain functional dynamics and BBB permeability in patients with RCVS. We prospectively recruited RCVS patients and healthy controls (HCs) from November 2016 to January 2023 in Headache Center in a tertiary medical center (> 3000 beds) and adjacent communities. RCVS patients who were diagnosed according to the International Headache Society criteria, and age- and sex-matched HCs were enrolled. Normalized entropy, derived from resting-state fMRI (rs-fMRI), was compared at the network and parcel levels between RCVS patients with and without BBB disruption. Dynamic contrast-enhanced MRI (DCE-MRI)-derived Ktrans BBB permeability and ultrasonographic findings were analyzed. In total, 188 subjects (100 RCVS + 88 HCs) were enrolled. Compared with the HCs, the RCVS patients had greater entropy (p = 0.014), which was greater in the RCVS patients without than in those with (adjusted p = 0.040) BBB disruption. Compared with HCs, patients without BBB disruption had greater entropy between 60 and 90 days after headache onset (adjusted p = 0.006). No significant differences in entropy were noted between disease stages in BBB-disrupted patients. Parcels within subnetworks of the Default mode network (Default A and C) exhibited higher entropy in patients without BBB disruption. In specific anatomical locations, entropy values were negatively correlated with ultrasonographic Lindegaard index vasoconstriction severity (p = 4.3 × 10- 6; within the Default A network) and DCE-MRI Ktrans BBB permeability (p = 0.005; within the Default C network). The differential changes in normalized entropy suggest that increased rs-fMRI signal complexity may reflect a compensatory functional response to abrupt vasoconstriction. In contrast, the loss of entropy fluctuations in the context of severe BBB disruption indicates a state of impaired cerebral autoregulation in patients with RCVS. The compensatory capacity decreased as vasoconstriction or BBB disruption exacerbated.

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