E. Bernd Ringelstein

Consensus on Microembolus Detection by TCD

Transcranial Doppler ultrasound is capable of detecting microembolic material, both gaseous and solid, within the intracranial cerebral arteries. To avoid discrediting this promising and exciting new technique, experts in this field met in January 1997 in Frankfurt, Germany, to discuss the limitations and problems of embolus detection and to determine guidelines for its proper use in clinical practice, as well as in scientific investigations. In particular, the authors suggest that studies report the following parameters: (1) ultrasound device, (2) transducer type and size, (3) insonated artery, (4) insonation depth, (5) algorithms for signal intensity measurement, (6) scale settings, (7) detection threshold, (8) axial extension of sample volume, (9) fast Fourier transform (FFT) size (number of points used), (10) FFT length (time), (11) FFT overlap, (12) transmitted ultrasound frequency, (13) high-pass filter settings, and (14) recording time. There was agreement that no current system of automatic embolus detection has the required sensitivity and specificity for clinical use.

Dual Antiplatelet Therapy With Clopidogrel and Aspirin in Symptomatic Carotid Stenosis Evaluated Using Doppler Embolic Signal Detection The Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) Trial

Background—Evidence for efficacy of dual antiplatelet therapy in stroke is limited. Symptomatic carotid stenosis patients are at high risk of early recurrent stroke. In this group, asymptomatic microembolic signals (MES), detected by transcranial Doppler ultrasound (TCD), are markers of future stroke and transient ischemic attack (TIA) risk. They offer a surrogate marker to evaluate antiplatelet therapy, but no multicenter study has evaluated the feasibility of this approach. Methods and Results—Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) is a randomized, double-blind study in subjects with recently symptomatic ≥50% carotid stenosis. Patients were screened with TCD, and if MES were detected, they were randomized to clopidogrel and aspirin or aspirin monotherapy. Repeated TCD recordings were made on days 2 and 7. MES were detected in 110 of 230 patients by online analysis at baseline, of whom 107 were randomized. Intention-to-treat analysis revealed a significant reduction in the primary end point: 43.8% of dual-therapy patients were MES positive on day 7, as compared with 72.7% of monotherapy patients (relative risk reduction 39.8%; 95% CI, 13.8 to 58.0; P=0.0046). The secondary end point of MES frequency per hour was reduced (compared with baseline) by 61.4% (95% CI, 31.6 to 78.2; P=0.0013) in the dual-therapy group at day 7 and by 61.6% (95% CI, 34.9 to 77.4; P=0.0005) on day 2. There were 4 recurrent strokes and 7 TIAs in the monotherapy group versus no stroke and 4 TIAs in the dual-therapy group that were treatment emergent and ipsilateral to the qualifying carotid stenosis; 2 additional ipsilateral TIAs occurred before treatment started. MES frequency was greater in the 17 patients with recurrent ipsilateral events compared with the 90 without (mean±SD: 24.4±27.7 versus 8.9±11.5 per hour; P=0.0003). Conclusions—In patients with recently symptomatic carotid stenosis, combination therapy with clopidogrel and aspirin is more effective than aspirin alone in reducing asymptomatic embolization. Doppler MES detection is a feasible method to evaluate the efficacy of antiplatelet therapy in multicenter studies.

A sequence variant in ZFHX3 on 16q22 associates with atrial fibrillation and ischemic stroke

We expanded our genome-wide association study on atrial fibrillation (AF) in Iceland, which previously identified risk variants on 4q25, and tested the most significant associations in samples from Iceland, Norway and the United States. A variant in the ZFHX3 gene on chromosome 16q22, rs7193343-T, associated significantly with AF (odds ratio OR = 1.21, P = 1.4 × 10−10). This variant also associated with ischemic stroke (OR = 1.11, P = 0.00054) and cardioembolic stroke (OR = 1.22, P = 0.00021) in a combined analysis of five stroke samples.

Cervical artery dissection—clinical features, risk factors, therapy and outcome in 126 patients

Abstract.The highly variable clinical course of cervical artery dissections still poses a major challenge to the treating physician. This study was conducted (1) to describe the differences in clinical and angiographic presentation of patients with carotid and vertebral artery dissections (CAD, VAD), (2) to define the circumstances that are related to bilateral arterial dissections, and (3) to determine factors that predict a poor outcome. Retrospectively and by standardised interview, we studied 126 patients with cervical artery dissections. Preceding traumata, vascular risk factors, presenting local and ischemic symptoms, and patientoutcome were evaluated. Patients with CAD presented more often with a partial Horner’s syndrome and had a higher prevalence of fibromuscular dysplasia than patients with VAD. Patients with VAD complained more often of neck pain, more frequently reported a preceding chiropractic manipulation and had a higher incidence of bilateral dissections than patients with CAD. Bilateral VAD was significantly related to a preceding chiropractic manipulation. Multivariate analysis showed that the variables stroke and arterial occlusion were the only independent factors associated with a poor outcome. This study emphasises the potential dangers of chiropractic manipulation of the cervical spine. Probably owing to the systematic use of forceful neck-rotation to both sides, this treatment was significantly associated with bilateral VAD. Patients with dissection-related cervical artery occlusion had a significantly increased risk of suffering a disabling stroke.

Genetic risk factors for ischaemic stroke and its subtypes (the METASTROKE collaboration): a meta-analysis of genome-wide association studies.

Summary Background Various genome-wide association studies (GWAS) have been done in ischaemic stroke, identifying a few loci associated with the disease, but sample sizes have been 3500 cases or less. We established the METASTROKE collaboration with the aim of validating associations from previous GWAS and identifying novel genetic associations through meta-analysis of GWAS datasets for ischaemic stroke and its subtypes. Methods We meta-analysed data from 15 ischaemic stroke cohorts with a total of 12 389 individuals with ischaemic stroke and 62 004 controls, all of European ancestry. For the associations reaching genome-wide significance in METASTROKE, we did a further analysis, conditioning on the lead single nucleotide polymorphism in every associated region. Replication of novel suggestive signals was done in 13 347 cases and 29 083 controls. Findings We verified previous associations for cardioembolic stroke near PITX2 (p=2·8×10−16) and ZFHX3 (p=2·28×10−8), and for large-vessel stroke at a 9p21 locus (p=3·32×10−5) and HDAC9 (p=2·03×10−12). Additionally, we verified that all associations were subtype specific. Conditional analysis in the three regions for which the associations reached genome-wide significance (PITX2, ZFHX3, and HDAC9) indicated that all the signal in each region could be attributed to one risk haplotype. We also identified 12 potentially novel loci at p<5×10−6. However, we were unable to replicate any of these novel associations in the replication cohort. Interpretation Our results show that, although genetic variants can be detected in patients with ischaemic stroke when compared with controls, all associations we were able to confirm are specific to a stroke subtype. This finding has two implications. First, to maximise success of genetic studies in ischaemic stroke, detailed stroke subtyping is required. Second, different genetic pathophysiological mechanisms seem to be associated with different stroke subtypes. Funding Wellcome Trust, UK Medical Research Council (MRC), Australian National and Medical Health Research Council, National Institutes of Health (NIH) including National Heart, Lung and Blood Institute (NHLBI), the National Institute on Aging (NIA), the National Human Genome Research Institute (NHGRI), and the National Institute of Neurological Disorders and Stroke (NINDS).

Microglial activation precedes and predominates over macrophage infiltration in transient focal cerebral ischemia: a study in green fluorescent protein transgenic bone marrow chimeric mice.

Resident microglia and hematogenous macrophages play crucial roles in the pathogenetic cascade following cerebral ischemia but may functionally differ regarding neuroprotective and cytotoxic properties. Distinction between these cells has not been possible due to a lack of discriminating cellular markers. We generated bone marrow chimeric mice by transplanting bone marrow from green fluorescent protein (GFP) transgenic mice into irradiated wild-type recipients. Transient focal cerebral ischemia was induced by transient middle cerebral artery occlusion (MCAO) for 30 min. Resident microglia and infiltrating macrophages were identified by immunohistochemistry and GFP fluorescence after 1-28 days. The first blood-derived cells infiltrating the infarct area were seen on Day 1 and identified as granulocytes. Hematogenous GFP(+) macrophages were rarely observed on Day 2, reached peak numbers on Day 7, and decreased thereafter. In contrast, resident GFP(-) microglial cells rapidly became activated already on Day 1 after MCAO. Even on Days 4 and 7, most macrophage-like cells remained GFP(-), indicating their derivation from resident microglia. Hematogenous macrophages were able to acquire a ramified morphology indistinguishable from resident microglia while microglial cells could develop into a phagocytic phenotype indistinguishable from infiltrating macrophages. The vast majority of macrophages in the infarct area are derived from local microglia, revealing a remarkable predominance of local defense mechanisms over immune cells arriving from the blood. GFP bone marrow chimeric mice are a powerful tool to further differentiate the function of resident microglia and hematogenous macrophages following cerebral ischemia.

Risk variants for atrial fibrillation on chromosome 4q25 associate with ischemic stroke

To find sequence variants that associate with the risk for ischemic stroke (IS), we performed a genome‐wide association study.

Atrial fibrillation in stroke-free patients is associated with memory impairment and hippocampal atrophy

AIMS To determine whether atrial fibrillation (AF) in stroke-free patients is associated with impaired cognition and structural abnormalities of the brain. AF contributes to stroke and secondary cognitive decline. In the absence of manifest stroke, AF can activate coagulation and cause cerebral microembolism which could damage the brain. METHODS AND RESULTS We cross-sectionally evaluated 122 stroke-free individuals with AF recruited locally within the German Competence Network on AF. As comparator, we recruited 563 individuals aged 37-84 years without AF from the same community. Subjects underwent 3 T magnetic resonance imaging to assess covert territorial brain infarction, white matter lesions, and brain volume measures. Subjects with evidence for stroke, dementia, or depression were excluded. Cognitive function was assessed by an extensive neuropsychological test battery covering the domains learning and memory, attention and executive functions, working memory, and visuospatial skills. Cognitive scores and radiographic measures were compared across individuals with and without AF by stepwise multiple regression models. Stroke-free individuals with AF performed significantly worse in tasks of learning and memory (ß = -0.115, P < 0.01) as well as attention and executive functions (ß = -0.105, P < 0.01) compared with subjects without AF. There was also a trend (P = 0.062) towards worse performance in learning and memory tasks in patients with chronic as compared with paroxysmal AF. Corresponding to the memory impairment, hippocampal volume was reduced in patients with AF. Other radiographic measures did not differ between groups. CONCLUSION Even in the absence of manifest stroke, AF is a risk factor for cognitive impairment and hippocampal atrophy. Therefore, cognition and measures of structural brain integrity should be considered in the evaluation of novel treatments for AF.

Mechanisms of acute cerebral infarctions in patients with middle cerebral artery stenosis: a diffusion-weighted imaging and microemboli monitoring study.

Although most therapeutic efforts and experimental stroke models focus on the concept of complete occlusion of the middle cerebral artery as a result of embolism from the carotid artery or cardiac chamber, relatively little is known about the stroke mechanism of intrinsic middle cerebral artery stenosis. Differences in stroke pathophysiology may require different strategies for prevention and treatment. We prospectively studied 30 consecutive acute ischemic stroke patients with middle cerebral artery stenosis detected by transcranial Doppler and magnetic resonance angiography. Patients underwent microembolic signal monitoring by transcranial Doppler and diffusion‐weighted magnetic resonance imaging. Characteristics of acute infarct on diffusion‐weighted magnetic resonance imaging were categorized according to the number (single or multiple infarcts) and the pattern of cerebral infarcts (cortical, border zone, or perforating artery territory infarcts). The data of microembolic signals and diffusion‐weighted magnetic resonance imaging were assessed blindly and independently by separate observers. Diffusion‐weighted magnetic resonance imaging showed that 15 patients (50%) had single acute cerebral infarcts and 15 patients had multiple acute cerebral infarcts. Among patients with multiple acute infarcts, unilateral, deep, chainlike border zone infarcts were the most common pattern (11 patients, 73%), and for single infarcts, penetrating artery infarcts were the most common (10 patients, 67%). Microembolic signals were detected in 10 patients (33%). The median number of microembolic signals per 30 minutes was 15 (range, 3–102). Microembolic signals were found in 9 patients with multiple infarcts and in 1 patient with a single infarct (p = 0.002, χ2). The number of microembolic signals predicted the number of acute infarcts on diffusion‐weighted magnetic resonance imaging (linear regression, adjusted R2 =0.475, p < 0.001). Common stroke mechanisms in patients with middle cerebral artery stenosis are the occlusion of a single penetrating artery to produce a small subcortical lacuna‐like infarct and an artery‐to‐artery embolism with impaired clearance of emboli that produces multiple small cerebral infarcts, especially along the border zone region.

Levodopa: Faster and better word learning in normal humans

Dopamine is a potent modulator of learning and has been implicated in the encoding of stimulus salience. Repetition, however, as required for the acquisition and reacquisition of sensorimotor or cognitive skills (e.g., in aphasia therapy), decreases salience. We here tested whether increasing brain levels of dopamine during repetitive training improves learning success. Forty healthy humans took 100mg of the dopamine precursor levodopa or placebo daily for 5 days in a randomized double‐blind and parallel‐group design. Ninety minutes later on each day, subjects were trained on an artificial vocabulary using a high‐frequency repetitive approach. Levodopa significantly enhanced the speed, overall success, and long‐term retention of novel word learning in a dose‐dependent manner. These findings indicate new ways to potentiate learning in a variety of domains if conventional training alone fails.