Cerebral microbleeds and hemodynamic changes in individuals with cognitive impairment

Background & Objective: Cerebral microbleeds (CMBs) are considered key markers of small vessel pathology linking mechanisms relating to ischemic and amyloid related vascular damage in Alzheimer disease (AD). We aim to investigate the differences of hemodynamic markers between patients with and without CMBs who presented with cognitive decline using transcranial Doppler (TCD) ultrasonography. Methods: We consecutively enrolled patients who were diagnosed with mild cognitive impairment (MCI) and probable AD dementia from May 2011 to December 2012. Using TCD ultrasonography, cerebrovascular reactivity (CVR) was evaluated with hyperventilation (HV) and breath-holding (BH) tests in addition to mean flow velocity (MFV) and pulsatility index (PI) of the middle cerebral artery. The number and location of CMBs were visually analyzed by two independent neurologists. Results: A total of 134 patients (probable AD, n=81; MCI, n=53) were enrolled in this study. Among them, 28 (20.9%) patients had CMBs; 18 (64.3%) lobar CMBs, 7 (25.0%) non-lobar CMBs. Patients with CMBs showed reduced MFV, higher resistance index value, and lower CVR compared with patients without CMBs after adjusting for age, vascular risk factors, and white matter hyperintensity. Multiple regression models showed that PI was dependent on age and presence of CMBs in frontal and parietal areas. CVR was closely associated with WMH severity and presence of CMBs in temporal. Conclusions: Our study showed that patients with CMBs had higher microvascular resistance and decreased cerebrovascular autoregulation compared to those without.