Cryptogenic stroke: time to determine aetiology

Fibrin-targeted PET probes for the detection of thrombi

There is an ongoing effort to develop better methods for noninvasive detection and characterization of thrombi. Here we describe the synthesis and evaluation of three new fibrin-targeted positron emission tomography (PET) probes (FBP1, FBP2, FBP3). Three fibrin-specific peptides were conjugated as 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-monoamides at the C- and N-termini and chelated with (64)CuCl2. Probes were prepared with a specific activity ranging from 10 to 130 μCi/nmol. Both the peptides and the probes exhibited nanomolar dissociation constants (Kd) for the soluble fibrin fragment DD(E), although the Cu-DOTA derivatization resulted in a 2-3 fold loss in affinity relative to the parent peptide. Biodistribution and imaging studies were performed in a rat model of carotid artery thrombosis. For FBP1 and FBP2 at 120 min post injection, the vessel containing the thrombus showed the highest concentration of radioactivity after the excretory organs, that is, the liver and kidneys. This was confirmed ex vivo by autoradiography, which showed >4-fold activity in the thrombus-containing artery compared to the contralateral artery. FBP3 showed much lower thrombus uptake, and the difference was traced to greater metabolism of this probe. Hybrid MR-PET imaging with FBP1 or FBP2 confirmed that these probes were effective for the detection of an arterial thrombus in this rat model. A thrombus was visible on PET images as a region of high activity that corresponded to a region of arterial occlusion identified by simultaneous MR angiography. FBP1 and FBP2 represent promising new probes for the molecular imaging of thrombi.

Patent foramen ovale, ischemic stroke and migraine: systematic review and stratified meta-analysis of association studies

BACKGROUND

Observational data have reported associations between patent foramen ovale (PFO), cryptogenic stroke and migraine. However, randomized trials of PFO closure do not demonstrate a clear benefit either because the underlying association is weaker than previously suggested or because the trials were underpowered. In order to resolve the apparent discrepancy between observational data and randomized trials, we investigated associations between (1) migraine and ischemic stroke, (2) PFO and ischemic stroke, and (3) PFO and migraine.

METHODS

Eligibility criteria were consistent; including all studies with specifically defined exposures and outcomes unrestricted by language. We focused on studies at lowest risk of bias by stratifying analyses based on methodological design and quantified associations using fixed-effects meta-analysis models.

RESULTS

We included 37 studies of 7,686 identified. Compared to reports in the literature as a whole, studies with population-based comparators showed weaker associations between migraine with aura and cryptogenic ischemic stroke in younger women (OR 1.4; 95% CI 0.9-2.0; 1 study), PFO and ischemic stroke (HR 1.6; 95 CI 1.0-2.5; 2 studies; OR 1.3; 95% CI 0.9-1.9; 3 studies), or PFO and migraine (OR 1.0; 95% CI 0.6-1.6; 1 study). It was not possible to look for interactions or effect modifiers. These results are limited by sources of bias within individual studies.

CONCLUSIONS

The overall pairwise associations between PFO, cryptogenic ischemic stroke and migraine do not strongly suggest a causal role for PFO. Ongoing randomized trials of PFO closure may need larger numbers of participants to detect an overall beneficial effect.

Clues to occult cancer in patients with ischemic stroke

Background

We hypothesized that hidden malignancy could be detected in patients with cryptogenic stroke without active cancer when they showed the distinctive characteristics of cancer-related stroke.

Methods and Findings

Among 2,562 consecutive patients with acute ischemic stroke, patients with cryptogenic stroke were analyzed and categorized into two groups according to the presence of active cancer: cryptogenic stroke with active cancer (cancer-related stroke, CA-stroke) group and without active cancer (CR-stroke) group. Patients with active lung cancer without stroke were also recruited for comparison purposes (CA-control). Clinical factors, lesion patterns on diffusion-weighted MRI (DWI), and laboratory findings were analyzed among groups. A total of 348 patients with cryptogenic stroke were enrolled in this study. Among them, 71 (20.4%) patients had active cancer at the time of stroke. The D-dimer levels were significantly higher in patients with CA-stroke than those with CR-stroke or CA-control (both p<0.001). Regarding lesion patterns, patients with CA-stroke mostly had multiple lesions in multiple vascular territories, while more than 80% of patients with CR-stroke had single/multiple lesions in a single vascular territory (P<0.001). D-dimer levels (OR 1.11 per 1 µg/mL increase; 95% CI 1.06–1.15; P<0.001) and DWI lesion patterns (OR 7.13; 95% CI 3.42–14.87; P<0.001) were independently associated with CA-stroke. Workup for hidden malignancy was performed during hospitalization in 10 patients who showed elevated D-dimer levels and multiple infarcts involving multiple vascular territories but had no known cancer, and it revealed hidden malignancies in all the patients.

Conclusion

Patients with CA-stroke have distinctive D-dimer levels and lesion patterns. These characteristics can serve as clues to occult cancer in patients with cryptogenic stroke.

RNA expression profiles from blood for the diagnosis of stroke and its causes

A blood test to detect stroke and its causes would be particularly useful in babies, young children, and patients in intensive care units and for emergencies when imaging is difficult to obtain or is unavailable. Whole genome microarrays were used to show specific gene expression profiles in rats 24 hours after ischemic and hemorrhagic stroke, hypoxia, and hypoglycemia. These proof-of-principle studies revealed that groups of genes (called gene profiles) can distinguish ischemic stroke patients from controls within 3 to 24 hours after the strokes. In addition, gene expression profiles have been developed that distinguish stroke due to large-vessel atherosclerosis from cardioembolic stroke. These profiles will be useful for predicting the causes of cryptogenic stroke. The results in adults suggest that similar diagnostic tools could be developed for children.

Fine particulate air pollution (PM2.5) and the risk of acute ischemic stroke

BACKGROUND

Short-term changes in levels of fine ambient particulate matter (PM2.5) may increase the risk of acute ischemic stroke; however, results from prior studies have been inconsistent. We examined this hypothesis using data from a multicenter prospective stroke registry.

METHODS

We analyzed data from 9202 patients hospitalized with acute ischemic stroke, having a documented date and time of stroke onset, and residing within 50 km of a PM2.5 monitor in 8 cities in Ontario, Canada. We evaluated the risk of ischemic stroke onset associated with PM2.5 in each city using a time-stratified case-crossover design, matching on day of week and time of day. We then combined these city-specific estimates using random-effects meta-analysis techniques. We examined whether the effects of PM2.5 differed across strata defined by patient characteristics and ischemic stroke etiology.

RESULTS

Overall, PM2.5 was associated with a -0.7% change in ischemic stroke risk per 10-μg/m increase in PM2.5 (95% confidence interval = -6.3% to 5.1%). These overall negative results were robust to a number of sensitivity analyses. Among patients with diabetes mellitus, PM2.5 was associated with an 11% increase in ischemic stroke risk (1% to 22%). The association between PM2.5 and ischemic stroke risk varied according to stroke etiology, with the strongest associations observed for strokes due to large-artery atherosclerosis and small-vessel occlusion.

CONCLUSIONS

These results do not support the hypothesis that short-term increases in PM2.5 levels are associated with ischemic stroke risk overall. However, specific patient subgroups may be at increased risk of particulate-related ischemic strokes.

A review of hereditary and acquired coagulation disorders in the aetiology of ischaemic stroke

The diagnostic workup in patients with ischaemic stroke often includes testing for prothrombotic conditions. However, the clinical relevance of coagulation abnormalities in ischaemic stroke is uncertain. Therefore, we reviewed what is presently known about the association between inherited and acquired coagulation disorders and ischaemic stroke, with a special emphasis on the methodological aspects. Good-quality data in this field are scarce, and most studies fall short on epidemiological criteria for causal inference. While inherited coagulation disorders are recognised risk factors for venous thrombosis, there is no substantial evidence for an association with arterial ischaemic stroke. Possible exceptions are the prothrombin G20210A mutation in adults and protein C deficiency in children. There is proof of an association between the antiphospholipid syndrome and ischaemic stroke, but the clinical significance of isolated mildly elevated antiphospholipid antibody titres is unclear. Evidence also suggests significant associations of increased homocysteine and fibrinogen concentrations with ischaemic stroke, but whether these associations are causal is still debated. Data on other acquired coagulation abnormalities are insufficient to allow conclusions regarding causality. For most coagulation disorders, a causal relation with ischaemic stroke has not been definitely established. Hence, at present, there is no valid indication for testing all patients with ischaemic stroke for these conditions. Large prospective population-based studies allowing the evaluation of interactive and subgroup effects are required to appreciate the role of coagulation disorders in the pathophysiology of arterial ischaemic stroke and to guide the management of individual patients.

Impaired transport function of the left atrium and left atrial appendage in cryptogenic stroke patients with atrial septal aneurysm and without patent foramen ovale

AIMS

Although atrial septal aneurysm (ASA) is frequently combined with patent foramen ovale and associated with cryptogenic stroke (CS), a pathophysiologic correlation between CS and ASA alone has not been fully elucidated. The aims of this study were to assess transport functions of the left atrium (LA) and left atrial appendage (LAA), and to evaluate their relationship in CS subjects with ASA alone.

METHODS AND RESULTS

This study consisted of 38 CS subjects with ASA alone and 38 matched controls. Transthoracic echocardiography including tissue Doppler imaging was performed in all subjects and transesophageal echocardiography was conducted in CS subjects to assess LAA emptying velocity (LAAev). We also measured soluble P- and E-selectin, interleukin-6 (IL-6), and high-sensitivity C-reactive protein (hs-CRP) as indices of prothrombogenic and proinflammatory activity. Although there were no differences in left ventricular functions and baseline characteristics between the two groups, CS subjects had significantly larger LA volume and lower LA active pump function compared with controls. LAAev was significantly correlated with LA active function. CS subjects had significantly higher E-selectin (P = 0.046), IL-6 (P = 0.040), and hs-CRP (P = 0.001) compared with controls.

CONCLUSIONS

Compared with controls, LA active pump function was significantly depressed and closely correlated with LAAev in CS subjects with ASA alone. Moreover, plasma levels of E-selectin, IL-6, and hs-CRP were significantly higher in CS subjects with ASA alone. These findings suggest that impaired LA and LAA functions are a crucial pathophysiologic mechanism for ischaemic stroke in subjects with ASA alone.

[Atrial fibrillation. New aspects for diagnosis and follow-up]

Continuous rhythm monitoring is the gold standard of objective rhythm assessment in patients with atrial fibrillation, thus, facilitating accurate detection of symptomatic and asymptomatic atrial fibrillation. This is of scientific and clinical interest for the understanding of this arrhythmia, the establishment of evidence-based therapeutic approaches, the definition of clinically indicated monitoring strategies, and for decision-making about oral anticoagulation. This article illustrates the importance of continuous monitoring of atrial fibrillation and presents developing technologies with their advantages and limitations as well as initial clinical experience.

Familial Mediterranean fever and central nervous system involvement: a case series

We conducted this study to determine familial Mediterranean fever (FMF)-associated central nervous system involvement including demyelinating lesions, stroke, and posterior reversible leukoencephalopathy syndrome (PRES). Patients with MEFV mutations were systematically reviewed through the Medical Biology Unit database. All samples sent for mutation analysis were screened for 10 common MEFV mutations. Patients with FMF and neurologic disorders according to the clinical records were invited for reevaluation. Lumbar puncture, electroencephalography, and evoked potentials were used to determine the type of neurologic involvement in selected cases. Electrocardiography, transthoracic and/or transesophageal echocardiography, and magnetic resonance imaging and/or angiography were performed to clarify the etiology of cerebrovascular disease. Of 8864 patients in the genetic testing database, 18 with neurologic signs were assessed. The mean age of patients was 31.0 +/- 11.8 years, mean age at first FMF symptom was 12.6 +/- 5.6 years, and mean age at neurologic involvement was 25.8 +/- 12.2 years. Fifty-five percent of patients were women. A homozygote MEFV mutation was detected in 16 of 18 patients (88.8%), and a homozygote M694V mutation was found in 72.2% of patients. We found 7 FMF patients with demyelinating lesions, 7 with cerebrovascular disease, and 4 with PRES. The mean interval between first FMF sign and neurologic involvement was 13.7 +/- 8.9 years in the demyelinating group, and 23.4 +/- 10.3 years in the group with cerebrovascular disease. Mean stroke age was 28.5 +/- 16.4 years. All patients in the PRES group had hypertension. Three different neurologic conditions in FMF patients were noticeable. Demyelinating lesions and cerebrovascular disease were the most common clinical presentations. Approximately 70% of patients had the homozygote M694V mutation. Neurologic involvement is rare but serious in FMF.

Molecular MRI of Thrombosis

This review focuses on recent approaches in using targeted MRI probes for noninvasive molecular imaging of thrombosis. Probe design strategies are discussed: choice of molecular target; nanoparticle versus small-molecule probe; and gadolinium versus iron oxide imaging reporter. Examples of these different design strategies are chosen from the recent literature. Novel contrast agents used to image direct and indirect binding to fibrin have been described as well as direct binding to activated platelets. Emphasis is placed on probes where utility has been demonstrated in animal models or in human clinical trials.

Altered fibrin clot structure/function in patients with cryptogenic ischemic stroke

BACKGROUND AND PURPOSE

We tested the hypothesis that fibrin structure/function is unfavorably altered in patients with cryptogenic ischemic stroke.

METHODS

Ex vivo plasma fibrin clot permeability, turbidimetry, and efficiency of fibrinolysis were determined in 89 patients with patent foramen ovale (PFO) and a history of first-ever stroke, 58 patients with first-ever stroke and no PFO, and 120 healthy controls.

RESULTS

Stroke patients, evaluated 3 to 19 months after the event, and controls did not differ with regard to age, sex, smoking, and fibrinogen. Stroke patients with or without PFO had lower clot permeability (P<0.0001), faster fibrin polymerization (P<0.0001), prolonged clot lysis time (P<0.0001), higher maximum D-dimer levels released from clots (P<0.0001), and maximum rate of D-dimer release (P=0.02) than controls. Time from stroke occurrence showed no association with any clot variables. Scanning electron microscopy of fibrin clots showed increased fiber diameter and density in stroke patients. Clots from stroke patients with PFO were more permeable and showed shorter lysis time compared to those without PFO, and this was related to lower proportion of smokers in the former group.

CONCLUSIONS

Altered fibrin clot structure and resistance to fibrinolysis are associated with cryptogenic stroke.