Cortical superficial siderosis: a marker of vascular amyloid in patients with cognitive impairment.

OBJECTIVE: To investigate the prevalence and associations of cortical superficial siderosis (cSS) utilizing MRI markers of cerebral small vessel disease and amyloid burden assessed through in vivo amyloid imaging in a cognitively impaired population.
METHODS: Gradient-recalled echo, T2*-weighted MRIs from 232 patients (Alzheimer disease-related cognitive impairment [ADCI], n = 90; subcortical vascular cognitive impairment [SVCI], n = 142) were reviewed for cSS. All subjects underwent in vivo amyloid imaging using [(11)C] Pittsburgh compound B (PiB)-PET. A multivariate logistic regression model was constructed to evaluate the predictive factors of cSS. A follow-up MRI was performed in 154 (66.4%) of 232 patients.
RESULTS: Twelve patients (5.2%) with cSS were equally distributed in ADCI (n = 6) and SVCI (n = 6) groups, but cSS was not present in any of the patients with a negative PiB scan. cSS was associated with markers of cerebral amyloid angiopathy, including higher global PiB retention ratio, APOE ε2 allele presence, and a strictly lobar distribution of cerebral microbleeds. Of those patients with baseline cSS, 33% showed progression over time; there were 2 cases of symptomatic intracranial hemorrhage.
CONCLUSIONS: cSS occurred in both ADCI and SVCI groups, but not in patients with amyloid-negative SVCI, supporting the hypothesis that cSS reflects an amyloid rather than ischemic etiology. The associations with strictly lobar cerebral microbleeds and APOE ε2 suggest that cerebral amyloid angiopathy, with increased vascular fragility related to APOE genotype, contributes to cSS in this population, with a high risk of progression over time and future intracranial hemorrhage.