Molecular Neuroimaging in Vascular Cognitive Impairment

Longitudinal tracing of neurochemical metabolic disorders in working memory neural circuit and optogenetics modulation in rats with vascular cognitive impairment

Chronic cerebral ischemia leads to vascular cognitive impairment (VCI) that exacerbates along with ischemia time and eventually develops into dementia. Recent advances in molecular neuroimaging contribute to understand its pathological characteristics. We previously traced the anisotropic diffusion of water molecules suggests that chronic cerebral ischemia leads to irreversible progressive damage to white matter integrity. However, the abnormalities of gray matter activity following chronic cerebral ischemia remains not entirely understood. In this study, in vivo hydrogen proton magnetic resonance spectroscopy (¹H-MRS) was applied to longitudinally track the neurochemical metabolic disorder of gray matter associated with working memory, and optogenetics modulation of neurochemical metabolism was performed for targeted treatment of VCI. The results showed that the concentration of N-acetylaspartate (NAA) in the right hippocampus, left hippocampus, right medial prefrontal cortex (mPFC) and mediodorsal thalamus was decreased as early as 7 days after chronic cerebral ischemia, subsequently gamma-aminobutyric acid (GABA) declined whereas myo-inositol (mI) and glutamate (Glu) increased at 14 days, as well as choline (Cho) lost at 28 days, concurrently the change of Glu and GABA in the mPFC and hippocampus was ischemia time-dependent manner within 1 month. Behaviorally, working memory and object recognition memory were impaired at 14 days, 28 days that significantly correlated with neurochemical metabolic disorders. Interestingly, using optogenetics modulation of PV neurons in the mPFC, the metabolic abnormalities of NAA and GABA in working memory neural circuit could be repaired after chronic cerebral ischemia, together with behavior improvements. These findings suggested that as early as 1∼4 weeks after chronic cerebral ischemia, the metabolism of NAA, Glu, mI and Cho was synchronously impaired in neural circuit of hippocampus-mediodorsal thalamus-mPFC, and the loss of GABA delayed in the hippocampus, and optogenetics modulation of parvalbumin (PV) neurons in the mPFC can improve the neurochemical metabolism of working memory neural circuit and enhance working memory.

A practical approach to the management of cerebral amyloid angiopathy

Cerebral amyloid angiopathy is a common small vessel disease in the elderly involving vascular amyloid-β deposition. Cerebral amyloid angiopathy is one of the leading causes of intracerebral hemorrhage and a significant contributor to age-related cognitive decline. The awareness of a diagnosis of cerebral amyloid angiopathy is important in clinical practice as it impacts decisions to use lifelong anticoagulation or nonpharmacological alternatives to anticoagulation such as left atrial appendage closure in patients who have concurrent atrial fibrillation, another common condition in older adults. This review summarizes the latest literature regarding the management of patients with sporadic cerebral amyloid angiopathy, including diagnostic criteria, imaging biomarkers for cerebral amyloid angiopathy severity, and management strategies to decrease intracerebral hemorrhage risk. In a minority of patients, the presence of cerebral amyloid angiopathy triggers an autoimmune inflammatory reaction, referred to as cerebral amyloid angiopathy-related inflammation, which is often responsive to immunosuppressive treatment in the acute phase. Diagnosis and management of cerebral amyloid angiopathy-related inflammation will be presented separately. While there are currently no effective therapeutics available to cure or halt the progression of cerebral amyloid angiopathy, we discuss emerging avenues for potential future interventions.

White matter atrophy in cerebral amyloid angiopathy

OBJECTIVE

We postulated that cerebral amyloid angiopathy (CAA) is associated with white matter atrophy (WMA) and that WMA can be related to cognitive changes in CAA.

METHODS

White matter volume expressed as percent of intracranial volume (pWMV) of prospectively enrolled patients without dementia diagnosed with probable CAA was compared to age-matched healthy controls (HC) and patients with Alzheimer disease (AD). Cognitive scores were also sought to understand the potential effects of WMA on cognitive function.

RESULTS

Patients with CAA (n = 72) had significantly lower pWMV (27.97% ± 2.63) when compared to age-matched HC (n = 72; mean difference [MD], 2.38%; p < 0.0001) and patients with AD (n = 72; MD, 1.57%; p < 0.0001). Differences were most pronounced in the posterior occipital regions in both comparisons. When comparisons were restricted to groups of patients with CAA but no intracerebral hemorrhage (n = 32) or hypertension (n = 32), and age-matched HC and AD, the significant differences were unaltered. Within the CAA cohort, higher age, lobar microbleed counts, and presence of hypertension were associated with lower pWMV (p = 0.0007, p = 0.031, and p = 0.003, respectively). All associations remained independent in multivariable analyses. Within the CAA cohort, higher pWMV independently correlated with better scores of executive function.

CONCLUSIONS

Patients with CAA show WMA when compared to age-matched HC and patients with AD. WMA independently correlates with the number of lobar microbleeds, a marker of CAA severity. Consistent spatial patterns of WMA especially in posterior regions might be related to CAA. The association between WMA and measures of executive function suggests that WMA might represent an important mediator of CAA-related neurologic dysfunction.

Superficial Cerebellar Microbleeds and Cerebral Amyloid Angiopathy

Background and Purpose—

The differentiation between cerebral amyloid angiopathy (CAA) and hypertensive small vessel disease in primary intracerebral hemorrhage is mainly based on hemorrhagic neuroimaging markers in the supratentorial regions, and the cause for cerebellar microbleeds remains unknown. Our aim was to investigate whether superficial cerebellar microbleeds are more likely to be related to CAA rather than hypertensive small vessel disease.

Methods—

Two hundred seventy-five consecutive patients with intracerebral hemorrhage were retrospectively reviewed from a prospectively maintained hospital-based stroke registry. Eighty-five (33.1%) patients had cerebellar microbleeds and were categorized into superficial (gray matter, vermis), deep (white matter, deep nucleus, cerebellar peduncle), or mixed type based on the location of cerebellar hemorrhagic lesions. Amyloid imaging was obtained using 11C-Pittsburgh Compound B–positron emission tomography in a subgroup of patients. The associations between cerebellar microbleed locations and the type of small vessel disease (CAA versus hypertensive small vessel disease) based on distribution of supratentorial hemorrhagic lesions as well as other magnetic resonance imaging and positron emission tomography markers were analyzed.

Results—

The presence of cerebellar microbleed was independently associated with supratentorial microbleed and lacunar infarcts (both P <0.01). Strictly superficial cerebellar microbleeds were significantly related to CAA–intracerebral hemorrhage, cortical superficial siderosis and high-grade enlarged perivascular space in centrum semiovale (all P <0.05); deep or mixed cerebellar microbleeds were related to hypertension and deep microbleed (all P <0.05). In multivariable models, superficial cerebellar microbleeds were independently associated with CAA–intracerebral hemorrhage ( P =0.03). Of 33 patients assessed by amyloid positron emission tomography, cerebral and cerebellar amyloid load (standardized uptake value ratio) was higher in patients with superficial cerebellar microbleeds compared with deep/mixed cerebellar microbleeds (cerebrum standardized uptake value ratio [reference: cerebellum] 1.33±0.24 versus 1.05±0.09, P <0.001; cerebellum standardized uptake value ratio [reference: pons] 0.58±0.08 versus 0.51±0.09, P =0.03).

Conclusions—

Patients with strictly superficial cerebellar microbleeds are associated with a clinicoradiological diagnosis of CAA as well as increased cerebral and cerebellar amyloid deposition on Pittsburgh Compound B–positron emission tomography, suggesting underlying CAA pathology.

Treatment Approaches to Lacunar Stroke

Lacunar strokes are appropriately named for their ability to cavitate and form ponds or "little lakes" (Latin: lacune -ae meaning pond or pit is a diminutive form of lacus meaning lake). They account for a substantial proportion of both symptomatic and asymptomatic ischemic strokes. In recent years, there have been several advances in the management of large vessel occlusions. New therapies such as non-vitamin K antagonist oral anticoagulants and left atrial appendage closure have recently been developed to improve stroke prevention in atrial fibrillation; however, the treatment of small vessel disease-related strokes lags frustratingly behind. Since Fisher characterized the lacunar syndromes and associated infarcts in the late 1960s, there have been no therapies specifically targeting lacunar stroke. Unfortunately, many therapeutic agents used for the treatment of ischemic stroke in general offer only a modest benefit in reducing recurrent stroke while adding to the risk of intracerebral hemorrhage and systemic bleeding. Escalation of antithrombotic treatments beyond standard single antiplatelet agents has not been effective in long-term lacunar stroke prevention efforts, unequivocally increasing intracerebral hemorrhage risk without providing a significant benefit. In this review, we critically review the available treatments for lacunar stroke based on evidence from clinical trials. For several of the major drugs, we summarize the adverse effects in the context of this unique patient population. We also discuss the role of neuroprotective therapies and neural repair strategies as they may relate to recovery from lacunar stroke.

Microangiopathy underlying mixed-location intracerebral hemorrhages/microbleeds: A PiB-PET study

OBJECTIVE

To test the hypothesis that patients with concomitant lobar and deep intracerebral hemorrhages/microbleeds (mixed ICH) have predominantly hypertensive small vessel disease (HTN-SVD) rather than cerebral amyloid angiopathy (CAA), using in vivo amyloid imaging.

METHODS

Eighty Asian patients with primary ICH without dementia were included in this cross-sectional study. All patients underwent brain MRI and 11C-Pittsburgh compound B (PiB)-PET imaging. The mean cortical standardized uptake value ratio (SUVR) was calculated using cerebellum as reference. Forty-six patients (57.5%) had mixed ICH. Their demographic and clinical profile as well as amyloid deposition patterns were compared to those of 13 patients with CAA-ICH and 21 patients with strictly deep microbleeds and ICH (HTN-ICH).

RESULTS

Patients with mixed ICH were younger (62.8 ± 11.7 vs 73.3 ± 11.9 years in CAA, p = 0.006) and showed a higher rate of hypertension than patients with CAA-ICH (p < 0.001). Patients with mixed ICH had lower PiB SUVR than patients with CAA (1.06 [1.01-1.13] vs 1.43 [1.06-1.58], p = 0.003). In a multivariable logistic regression model, mixed ICH was associated with hypertension (odds ratio 8.9, 95% confidence interval 1.4-58.4, p = 0.02) and lower PiB SUVR (odds ratio 0.03, 95% confidence interval 0.001-0.87, p = 0.04) compared to CAA after adjustment for age. Compared to HTN-ICH, mixed ICH showed a similar mean age (62.8 ± 11.7 vs 60.1 ± 14.5 years in HTN-ICH) and risk factor profile (all p > 0.1). Furthermore, PiB SUVR did not differ between mixed ICH (values presented above) and HTN-ICH (1.10 [1.00-1.16], p = 0.45).

CONCLUSIONS

Patients with mixed ICH have much lower amyloid load than patients with CAA-ICH, while being similar to HTN-ICH. Overall, mixed ICH is probably caused by HTN-SVD, an important finding with clinical relevance.

Updates on Prevention of Hemorrhagic and Lacunar Strokes

Intracerebral hemorrhage (ICH) and lacunar infarction (LI) are the major acute clinical manifestations of cerebral small vessel diseases (cSVDs). Hypertensive small vessel disease, cerebral amyloid angiopathy, and hereditary causes, such as Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), constitute the three common cSVD categories. Diagnosing the underlying vascular pathology in these patients is important because the risk and types of recurrent strokes show significant differences. Recent advances in our understanding of the cSVD-related radiological markers have improved our ability to stratify ICH risk in individual patients, which helps guide antithrombotic decisions. There are general good-practice measures for stroke prevention in patients with cSVD, such as optimal blood pressure and glycemic control, while individualized measures tailored for particular patients are often needed. Antithrombotic combinations and anticoagulants should be avoided in cSVD treatment, as they increase the risk of potentially fatal ICH without necessarily lowering LI risk in these patients. Even when indicated for a concurrent pathology, such as nonvalvular atrial fibrillation, nonpharmacological approaches should be considered in the presence of cSVD. More data are emerging regarding the presentation, clinical course, and diagnostic markers of hereditary cSVD, allowing accurate diagnosis, and therefore, guiding management of symptomatic patients. When suspicion for asymptomatic hereditary cSVD exists, the pros and cons of prescribing genetic testing should be discussed in detail in the absence of any curative treatment. Recent data regarding diagnosis, risk stratification, and specific preventive approaches for both sporadic and hereditary cSVDs are discussed in this review article.

Mixed-location cerebral hemorrhage/microbleeds: Underlying microangiopathy and recurrence risk

OBJECTIVE

To assess the predominant type of cerebral small vessel disease (SVD) and recurrence risk in patients who present with a combination of lobar and deep intracerebral hemorrhage (ICH)/microbleed locations (mixed ICH).

METHODS

Of 391 consecutive patients with primary ICH enrolled in a prospective registry, 75 (19%) had mixed ICH. Their demographics, clinical/laboratory features, and SVD neuroimaging markers were compared to those of 191 patients with probable cerebral amyloid angiopathy (CAA-ICH) and 125 with hypertensive strictly deep microbleeds and ICH (HTN-ICH). ICH recurrence and case fatality were also analyzed.

RESULTS

Patients with mixed ICH showed a higher burden of vascular risk factors reflected by a higher rate of left ventricular hypertrophy, higher creatinine values, and more lacunes and severe basal ganglia (BG) enlarged perivascular spaces (EPVS) than patients with CAA-ICH (all p < 0.05). In multivariable models mixed ICH diagnosis was associated with higher creatinine levels (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.2-5.0, p = 0.010), more lacunes (OR 3.4, 95% CI 1.7-6.8), and more severe BG EPVS (OR 5.8, 95% CI 1.7-19.7) than patients with CAA-ICH. Conversely, when patients with mixed ICH were compared to patients with HTN-ICH, they were independently associated with older age (OR 1.03, 95% CI 1.02-1.1), more lacunes (OR 2.4, 95% CI 1.1-5.3), and higher microbleed count (OR 1.6, 95% CI 1.3-2.0). Among 90-day survivors, adjusted case fatality rates were similar for all 3 categories. Annual risk of ICH recurrence was 5.1% for mixed ICH, higher than for HTN-ICH but lower than for CAA-ICH (1.6% and 10.4%, respectively).

CONCLUSIONS

Mixed ICH, commonly seen on MRI obtained during etiologic workup, appears to be driven mostly by vascular risk factors similar to HTN-ICH but demonstrates more severe parenchymal damage and higher ICH recurrence risk.

Association of Key Magnetic Resonance Imaging Markers of Cerebral Small Vessel Disease With Hematoma Volume and Expansion in Patients With Lobar and Deep Intracerebral Hemorrhage

Importance

Hematoma expansion is an important determinant of outcome in spontaneous intracerebral hemorrhage (ICH) due to small vessel disease (SVD), but the association between the severity of the underlying SVD and the extent of bleeding at the acute phase is unknown to date.

Objective

To investigate the association between key magnetic resonance imaging (MRI) markers of SVD (as per the Standards for Reporting Vascular Changes on Neuroimaging [STRIVE] guidelines) and hematoma volume and expansion in patients with lobar or deep ICH.

Design, Setting, and Participants

Analysis of data collected from 418 consecutive patients admitted with primary lobar or deep ICH to a single tertiary care medical center between January 1, 2000, and October 1, 2012. Data were analyzed on March 4, 2016. Participants were consecutive patients with computed tomographic images allowing ICH volume calculation and MRI allowing imaging markers of SVD assessment.

Main Outcomes and Measures

The ICH volumes at baseline and within 48 hours after symptom onset were measured in 418 patients with spontaneous ICH without anticoagulant therapy, and hematoma expansion was calculated. Cerebral microbleeds, cortical superficial siderosis, and white matter hyperintensity volume were assessed on MRI. The associations between these SVD markers and ICH volume, as well as hematoma expansion, were investigated using multivariable models.

Results

This study analyzed 254 patients with lobar ICH (mean [SD] age, 75 [11] years and 140 [55.1%] female) and 164 patients with deep ICH (mean [SD] age 67 [14] years and 71 [43.3%] female). The presence of cortical superficial siderosis was an independent variable associated with larger ICH volume in the lobar ICH group (odds ratio per quintile increase in final ICH volume, 1.49; 95% CI, 1.14-1.94; P = .004). In multivariable models, the absence of cerebral microbleeds was associated with larger ICH volume for both the lobar and deep ICH groups (odds ratios per quintile increase in final ICH volume, 1.41; 95% CI, 1.11-1.81; P = .006 and 1.43; 95% CI, 1.04-1.99; P = .03; respectively) and with hematoma expansion in the lobar ICH group (odds ratio, 1.70; 95% CI, 1.07-2.92; P = .04). The white matter hyperintensity volumes were not associated with either hematoma volume or expansion.

Conclusions and Relevance

In patients admitted with primary lobar or deep ICH to a single tertiary care medical center, the presence of cortical superficial siderosis was an independent variable associated with larger lobar ICH volume, and the absence of cerebral microbleeds was associated with larger lobar and deep ICHs. The absence of cerebral microbleeds was independently associated with more frequent hematoma expansion in patients with lobar ICH. We provide an analytical framework for future studies aimed at limiting hematoma expansion.

Intravoxel Incoherent Motion Imaging in Small Vessel Disease: Microstructural Integrity and Microvascular Perfusion Related to Cognition

BACKGROUND AND PURPOSE

Cerebral small vessel disease (SVD) is associated with cognitive impairment. This may be because of decreased microstructural integrity and microvascular perfusion, but data on these relationships are scarce. We determined the relationship between cognition and microvascular perfusion and microstructural integrity in SVD patients, using intravoxel incoherent motion imaging-a diffusion-weighted magnetic resonance imaging technique designed to determine microvascular perfusion and microstructural integrity simultaneously.

METHODS

Seventy-three patients with SVD and 39 controls underwent intravoxel incoherent motion imaging and neuropsychological assessment. Parenchymal diffusivity D (a surrogate measure of microstructural integrity) and perfusion-related measure fD* were calculated for the normal appearing white matter, white matter hyperintensities, and cortical gray matter. The associations between cognitive performance and D and fD* were determined.

RESULTS

In SVD patients, multivariable analysis showed that lower fD* in the normal appearing white matter and cortical gray matter was associated with lower overall cognition (P=0.03 and P=0.002, respectively), lower executive function (P=0.04 and P=0.01, respectively), and lower information-processing speed (P=0.04 and P=0.01, respectively). D was not associated with cognitive function. In controls, no association was found between D, fD*, and cognition.

CONCLUSIONS

In SVD patients, lower cognitive performance is associated with lower microvascular perfusion in the normal appearing white matter and cortical gray matter. Our results support recent findings that both cortical gray matter and normal appearing white matter perfusion may play a role in the pathophysiology of cognitive dysfunction in SVD.

CLINICAL TRIAL REGISTRATION

URL: http://www.trialregister.nl. Unique identifier: NTR3786.

Florbetapir-PET to diagnose cerebral amyloid angiopathy: A prospective study

OBJECTIVE

We hypothesized that florbetapir, a Food and Drug Administration-approved PET tracer, could distinguish cerebral amyloid angiopathy (CAA)-related intracerebral hemorrhage (ICH) from hypertensive ICH (HTN-ICH).

METHODS

We prospectively enrolled survivors of primary ICH related to probable CAA (per Boston Criteria, n = 10) and HTN-ICH (n = 9) without dementia. All patients underwent florbetapir-PET and multimodal MRI, and patients with CAA had additional Pittsburgh compound B (PiB) PET. Amyloid burden was assessed quantitatively (standard uptake value ratio [SUVR]) and visually classified as positive or negative.

RESULTS

The CAA and HTN-ICH groups had similar age (66.9 vs 67.1), sex, and leukoaraiosis volumes (31 vs 30 mL, all p > 0.8). Florbetapir uptake and PiB retention strongly correlated in patients with CAA both globally within cerebral cortex (r = 0.96, p < 0.001) and regionally in lobar cortices (all r > 0.8, all p ≤ 0.01). Mean global cortical florbetapir uptake was substantially higher in CAA than HTN-ICH (SUVR: 1.41 ± 0.17 vs 1.15 ± 0.08, p = 0.001), as was mean occipital SUVR (1.44 ± 0.12 vs 1.17 ± 0.08, p < 0.001), even after correcting for global SUVR (p = 0.03). Visual rating for positive/negative florbetapir demonstrated perfect interrater agreement (k = 1) and was positive for all 10 patients with CAA vs 1 of 9 HTN-ICH patients (sensitivity 100%, specificity 89%).

CONCLUSIONS

Florbetapir appears to label vascular amyloid in patients with CAA-related ICH. The approved florbetapir binary visual reading method can have diagnostic value in appropriate clinical settings.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that florbetapir-PET provides a sensitivity of 100% (95% confidence interval [CI] 66%-100%) and specificity of 89% (95% CI 51%-99%) for determination of probable CAA among cognitively normal patients.