Cerebral Amyloid Angiopathy-Related Inflammation and Biopsy-Positive Primary Angiitis of the CNS: A Comparative Study

Amyloid-related imaging abnormalities: manifestations, metrics and mechanisms

Three monoclonal antibodies directed against specific forms of the amyloid-β (Aβ) peptide have been granted accelerated or traditional approval by the FDA as treatments for Alzheimer disease, representing the first step towards bringing disease-modifying treatments for this disease into clinical practice. Here, we review the detection, underlying pathophysiological mechanisms and clinical implications of amyloid-related imaging abnormalities (ARIA), the most impactful adverse effect of anti-Aβ immunotherapy. ARIA appears as regions of oedema or effusions (ARIA-E) in brain parenchyma or sulci or as haemorrhagic lesions (ARIA-H) in the form of cerebral microbleeds, convexity subarachnoid haemorrhage, cortical superficial siderosis or intracerebral haemorrhage. Analysis of the radiographic appearance of ARIA, its clinical risk factors and underlying neuropathology, and results from animal models point to a central role for cerebral amyloid angiopathy - a condition characterized by cerebrovascular Aβ deposits - as a key component, either as a direct target for antibody-mediated inflammation or as recipient of Aβ mobilized from plaques in the Alzheimer brain parenchyma. The great majority of ARIA occurrences are associated with mild or no clinical symptoms. However, ~5% of all ARIA events are severe enough to result in hospitalization, permanent disability or death and thus raise challenging clinical questions regarding patient selection and use of concomitant agents. Therefore, identifying novel approaches to predicting, modelling, preventing and treating ARIA remains a key step towards allowing safe use of anti-Aβ immunotherapy for the world's rapidly ageing population.

Clinical and Neuroradiological Manifestations of Cerebral Amyloid Angiopathy: A Closer Look into the Natural History of a Frequent Disease

Cerebral amyloid angiopathy (CAA) is one of the most prevalent small vessel diseases (SVDs). Its neuroradiological hallmarks are both hemorrhagic and non-hemorrhagic ones. Among the clinical manifestations, transient focal neurological episodes (TFNEs) are associated with an increased risk of bleeding in a short time period and with convexal subarachnoid hemorrhage (SAH). The natural history of CAA is incompletely characterized in the literature, because the focus has been mostly on hemorrhagic events, while both clinical and non-hemorrhagic presentations are possible and sometimes underestimated. Furthermore, new diagnostic criteria have incorporated non-hemorrhagic Magnetic Resonance Imaging (MRI) markers and non-hemorrhagic clinical presentations. Disease trajectories are often individual and help provide food for thought and discussion on some issues, thus allowing for a greater and deeper evaluation. We, therefore, present a case that exemplifies how the natural history of CAA can be atypical compared to its expected course, which is long and not only hemorrhagic. Several episodes of CAA-related inflammation, with prevalent, but not exclusive, leptomeningeal involvement, were evaluated and treated in the presented case, in which the intraparenchymal cerebral hemorrhagic manifestation was the last in the patient's history. CAA may have a very long natural history. During the disease's course, inflammatory features might be prominent in neuroimaging but not strongly symptomatic, and intraparenchymal cerebral hemorrhage (ICH) may be a late event. The awareness of this subtype of the disease allows us to better explore the pathophysiology of CAA and to increase the level of clinical suspicion for the diagnosis. Furthermore, the distinction between different disease phenotypes can provide useful information for patient management in clinical practice.

Cerebral amyloid angiopathy: one single entity?

PURPOSE OF REVIEW

Cerebral amyloid angiopathy (CAA) is a common brain disorder among the elderly and individuals with Alzheimer's disease, where accumulation of amyloid-ß can lead to intracerebral hemorrhage and dementia. This review discusses recent developments in understanding the pathophysiology and phenotypes of CAA.

RECENT FINDINGS

CAA has a long preclinical phase starting decades before symptoms emerge. Its pathophysiology follows consecutive stages of amyloid-ß deposition, decreased vascular reactivity, nonhemorrhagic changes, and ultimately hemorrhages. Although impaired perivascular clearance is the leading hypothesis underlying CAA, several lines of evidence suggest that glymphatic dysfunction also plays a significant role in the disease process. Despite its common pathway, the disease course is variable. Some patients develop more microbleeds, while others develop larger hemorrhages, suggesting a differentiation in vascular remodeling. Some patients with CAA develop a symptomatic immune response, and inflammation could be an important contributor to vascular damage in CAA in general. Furthermore, the prion-like transmission of amyloid-β has been identified as a cause of iatrogenic CAA occurring decades after neurosurgical procedures involving cadaveric dura mater.

SUMMARY

Emerging evidence of sporadic, hereditary, inflammatory, and iatrogenic CAA suggests a complex interplay between brain clearance, inflammation and vascular remodeling leading to a diverse clinical phenotype.

No replicating evidence for anti-amyloid-β autoantibodies in cerebral amyloid angiopathy-related inflammation

OBJECTIVE

Elevated levels of anti-amyloid-β (anti-Aβ) autoantibodies in cerebrospinal fluid (CSF) have been proposed as a diagnostic biomarker for cerebral amyloid angiopathy-related inflammation (CAA-RI). We aimed to independently validate the immunoassay for quantifying these antibodies and evaluate its diagnostic value for CAA-RI.

METHODS

We replicated the immunoassay to detect CSF anti-Aβ autoantibodies using CSF from CAA-RI patients and non-CAA controls with unrelated disorders and further characterized its performance. Moreover, we conducted a literature review of CAA-RI case reports to investigate neuropathological and CSF evidence of the nature of the inflammatory reaction in CAA-RI.

RESULTS

The assay demonstrated a high background signal in CSF, which increased and corresponded with higher total immunoglobulin G (IgG) concentration in CSF (rsp = 0.51, p = 0.02). Assay levels were not elevated in CAA-RI patients (n = 6) compared to non-CAA controls (n = 20; p = 0.64). Literature review indicated only occasional presence of B-lymphocytes and plasma cells (i.e., antibody-producing cells), alongside the abundant presence of activated microglial cells, T-cells, and other monocyte lineage cells. CSF analysis did not convincingly indicate intrathecal IgG production.

INTERPRETATION

We were unable to reproduce the reported elevation of anti-Aβ autoantibody concentration in CSF of CAA-RI patients. Our findings instead support nonspecific detection of IgG levels in CSF by the assay. Reviewed CAA-RI case reports suggested a widespread cerebral inflammatory reaction. In conclusion, our findings do not support anti-Aβ autoantibodies as a diagnostic biomarker for CAA-RI.

Clinical recommendations for non-invasive ultrasound neuromodulation

Non-invasive ultrasound neuromodulation has experienced exponential growth in the neuroscientific literature, recently also including clinical studies and applications. However, clinical recommendations for the secure and effective application of ultrasound neuromodulation in pathological brains are currently lacking. Here, clinical experts with neuroscientific expertise in clinical brain stimulation and ultrasound neuromodulation present initial clinical recommendations for ultrasound neuromodulation with relevance for all ultrasound neuromodulation techniques. The recommendations start with methodological safety issues focusing on technical issues to avoid harm to the brain. This is followed by clinical safety issues focusing on important factors concerning pathological situations.