Ischemic lesions and superficial siderosis in CAA: Partners in crime or innocent bystanders?

Cerebral amyloid angiopathy (CAA), first described in 1927 as a congophilic angiopathy associated with amyloid plaque in brains of patients with Alzheimer dementia,1 has an association with large and small intracranial hemorrhages (ICH). The differential diagnosis of ICH therefore includes CAA, especially in older patients or those without hypertension. The widely used Boston Criteria for diagnosis of CAA in vivo rely on the hemorrhagic characteristics of the disease.2 The pathophysiology of ICH in CAA remains uncertain. Thus, its prognosis, risk stratification, and clinical management present a challenge. Additional imaging features of CAA have contributed potential new perspectives on pathophysiology. The report of ischemic lesions in CAA may represent a novel concept for most clinicians accustomed to thinking about CAA as a hemorrhagic disease. The observation that Alzheimer dementia brains with severe amyloid angiopathy had more prevalent infarcts3–5 prompted subsequent investigations suggesting that amyloid deposition in small and medium-sized cortical vessels may play an active role in ischemia through pathologic thickening of the vessel wall, producing reduction or obliteration of the vessel lumen.6,7 Cortical superficial siderosis (cSS), easy to detect with modern MRI, is a striking and common feature of CAA. How these additional imaging features fit into a larger model of CAA remains unclear. Are they an epiphenomenon or can they teach us about the disease? In the current issue of Neurology® , a pair of articles suggest that CAA might be a multifaceted vascular entity in its own right, and elucidation of these newer features may increase our understanding of its pathophysiology, leading to better prognosis and management.