Subarachnoid hemorrhage (SAH) carries high mortality and disability rates, which are substantially driven by complications. Early brain injury and vasospasm can happen after SAH and are crucial events to prevent and treat to improve prognosis. In recent decades, immunological mechanisms have been implicated in SAH complications, with both innate and adaptive immunity involved in mechanisms of damage after SAH. The purpose of this review is to summarize the immunological profile of vasospasm, highlighting the potential implementation of biomarkers for its prediction and management. Overall, the kinetics of central nervous system (CNS) immune invasion and soluble factors’ production critically differs between patients developing vasospasm compared to those not experiencing this complication. In particular, in people developing vasospasm, a neutrophil increase develops in the first minutes to days and pairs with a mild depletion of CD45+ lymphocytes. Cytokine production is boosted early on after SAH, and a steep increase in interleukin-6, metalloproteinase-9 and vascular endothelial growth factor (VEGF) anticipates the development of vasospasm after SAH. We also highlight the role of microglia and the potential influence of genetic polymorphism in the development of vasospasm and SAH-related complications.

Background: The transmission of amyloid β (Aβ) in humans leading to iatrogenic cerebral amyloid angiopathy (iCAA) is a novel concept with analogies to prion diseases. However, the number of published cases is low, and larger international studies are missing. Aims: We aimed to build a large multinational collaboration on iCAA to better understand the clinical spectrum of affected patients. Methods: We collected clinical data on patients with iCAA from Austria, Croatia, Italy, Slovenia, and Spain. Patients were included if they met the proposed Queen Square diagnostic criteria (QSC) for iCAA. In addition, we pooled data on disease onset, latency, and cerebrospinal fluid (CSF) biomarkers from previously published iCAA cases based on a systematic literature review. Results: Twenty-seven patients (22% women) were included in this study. Of these, 19 (70%) met the criteria for probable and 8 (30%) for possible iCAA. Prior neurosurgical procedures were performed in all patients (93% brain surgery, 7% spinal surgery) at median age of 8 (interquartile range (IQR) = 4–18, range = 0–26 years) years. The median symptom latency was 39 years (IQR = 34–41, range = 28–49). The median age at symptom onset was 49 years (IQR = 43–55, range = 32–70). Twenty-one patients (78%) presented with intracranial hemorrhage and 3 (11%) with seizures. Conclusions: Our large international case series of patients with iCAA confirms a wide age boundary for the diagnosis of iCAA. Dissemination of awareness of this rare condition will help to identify more affected patients.

Background: We aimed to describe neuroimaging features, clinical profiles and long-term outcomes in patients with iatrogenic cerebral amyloid angiopathy (iCAA).Methods: We performed a systematic literature search for case series of iCAA and included individual patients and their longitudinal clinical and neuroimaging data in this pooled cohort study. Patients meeting a modified version of the Queen Square criteria for iCAA were included. Baseline and follow-up MRIs were centrally analysed for markers of CAA using validated rating scales.Results: We included 51 patients (68.6% male, median age at presentation 48 years), 51.0% with probable and 49.0% with possible iCAA. We evaluated 219 MRIs acquired over a median follow-up time of 3.7 years (IQR 1.8–6.4). There were 43 symptomatic intracerebral haemorrhages (ICH) in 24 patients during follow-up, a rate of 16.7 per 100 patient-years.Patients with previous supratentorial brain surgery had an ipsilateral-dominant distribution and spread of haemorrhagic markers on MRI. 14/51 (27.5%) patients had transient inflammatory changes (cortical or parenchymal oedema, sulcal hyperintensities). Haemorrhagic markers progressed during follow-up. In addition to 43 symptomatic ICH, 36 asymptomatic ICH (mostly smaller intragyral haemorrhages) were detected on follow-up scans. Besides numerous lobar microbleeds (median 16 at baseline, 53 at last follow-up), deep microbleeds were present in 19.6% of patients at baseline and 44.4% at follow-up. Severe perivascular spaces in centrum semiovale were common at baseline (64.7%) and follow-up (95.6%).Conclusions: Patients with iCAA appear to have distinctive MRI characteristics, which might differentiate iCAA from other CAA subtypes and provide new insights into underlying disease mechanisms.

Cerebral amyloid angiopathy (CAA)-related features on neuroimaging often coexist with signs of arteriolosclerosis-small vessel disease on neuroimaging in people with intracranial hemorrhage (ICH). This study aimed at defining the value of amyloid pathology detected by ^18Fflutemetamol PET in reclassification and stratification of risk of bleeding in people with mixed CAA-arteriolosclerosis features. We included consecutive patients admitted to 2 institutions (2018-2023) with spontaneous symptomatic ICH, subarachnoid hemorrhage (SAH), transient focal neurologic episodes (TFNE), or cognitive impairment and MRI showing CAA hallmarks. All patients underwent brain magnetic resonance imaging (MRI) with susceptibility weighted imaging and ^18Fflutemetamol PET imaging and were followed up for at least 1 year. We compared cases with CAA and arteriolosclerosis + CAA features and defined long-term outcomes (composite outcome including death, ICH, ischemic stroke, SAH, TFNE) depending on PET status (CAA/amyloid pathology vs arteriolosclerosis-predominant groups). Among 47 patients, according to PET and MRI imaging, 38 patients were reclassified in the CAA/amyloid pathology group and 9 in the arteriolosclerosis-predominant group, with similar cardiovascular risk factors but a significantly higher lobar microbleed burden for the former group. The CAA/amyloid pathology group had higher rates of composite outcome (43.9 vs 11.1 events per 100 patient-year; p = 0.039) and ICH (36.5 vs 5.6 events per 100 patient-years; p = 0.04) compared with the arteriolosclerosis-predominant group. ^18FFlutemetamol PET imaging can help in reclassification of mixed arteriolosclerosis + CAA into CAA/amyloid pathology and arteriolosclerosis-predominant, with implications on long-term risk of recurrent events. This study provides Class IV evidence that ^18Fflutemetamol PET can distinguish between CAA + arteriolosclerosis and arteriolosclerosis-predominant pathology.

Recently, a subset of patients affected by cerebral amyloid angiopathy (CAA) distinguished by atypical juvenile onset and a hypothesized iatrogenic origin (iatrogenic CAA, iCAA) has emerged. β-Amyloid (Aβ) accumulation evidenced by amyloid PET positivity or CSF Aβ decrease was included in the iCAA diagnostic criteria. Conversely, diagnostic criteria for sporadic CAA (sCAA) do not involve biomarker analysis. The aim of this study was to assess CSF and plasma levels of Aβ and tau in iCAA and sCAA cohorts. Patients affected by probable or possible CAA according to established criteria (Boston 2.0) were prospectively recruited at Fondazione IRCCS Carlo Besta and San Gerardo dei Tintori from May 2021 to January 2024. Patients with probable and possible iCAA or sCAA with available plasma and/or CSF samples were included. Clinical and neurologic data were collected, and levels of Aβ40, Aβ42, total tau, and phospho-tau (p-tau) were assessed in CSF and plasma by SiMoA and Lumipulse. 21 patients with iCAA (72% male, mean age at symptom onset 50 years [36-74]) and 32 patients with sCAA (44% male, mean age at symptom onset 68 years [52-80]) were identified. Cognitive impairment and cardiovascular risk factors in the sCAA cohort were more common compared with the iCAA cohort. Patients with sCAA and iCAA showed similar CSF levels for Aβ40 (p = 0.5 [sCAA, 95% CI 2,604-4,228; iCAA, 95% CI 1,958-3,736]), Aβ42 (p = 0.7 [sCAA, 95% CI 88-157; iCAA, 95% CI 83-155]), and total tau (p = 0.08 [sCAA, 95% CI 80-134; iCAA, 95% CI 37-99]). Plasma levels of Aβ40 (p = 0.08, 95% CI 181-222), Aβ42 (p = 0.3, 95% CI 6-8), and total tau (p = 0.4, 95% CI 3-6) were not statistically different in patients with sCAA compared with iCAA ones (Aβ40, 95% CI 153-193; Aβ42, 95% CI 6-7 and total tau, 95% CI 2-4). Despite presenting with a younger age at onset, fewer cardiovascular risk factors, and lower cognitive impairment, patients with iCAA demonstrated Aβ and tau levels comparable with elderly patients with sCAA, supporting a common molecular paradigm between the 2 CAA forms.