BACKGROUND AND PURPOSE: Vascular aspects like global cerebral hypoperfusion are frequently reported in patients with multiple sclerosis (MS). Although mechanistic question remains unanswered, this hemodynamic impairment may be caused by a widespread endothelial dysfunction. Furthermore, impaired cerebrovascular reactivity (CVR) has been described in patients with MS by means of hypercapnic perfusion magnetic resonance imaging (MRI). We sought to further evaluate potential hemodynamic restriction in patients with MS using functional sonographic methods.METHODS: We evaluated consecutive patients with MS and healthy controls with adequate bilateral transtemporal window. CVR was assessed by bilateral transcranial Doppler monitoring of proximal middle cerebral arteries. Mean flow velocities were recorded before and after 30 seconds of breath holding. Vasomotor response was quantified by breath holding index (BHI).RESULTS: A total of 42 patients with MS (mean age 39 ± 12 years; 69% women) were compared to 31 healthy controls (mean age 35 ± 11 years; 71% women). BHI was lower in patients with MS compared to healthy controls (.70 ± .43 vs. .93 ± .55; P = .006), documenting a lower cerebrovascular response to hypercapnia. There was no correlation between patient age (r = .1254; P = .277), expanded disability status scale (r = .1838; P = .109), and disease duration (r = .1882; P = .101) with BHI in patients with MS.CONCLUSIONS: These preliminary sonographic findings appear to independently corroborate the previously reported observation of impaired CVR on brain MRI in patients with MS. However, the underlying pathophysiological mechanisms as well as the clinical impact of this observation remain elusive.