Purpose We investigated the frequency and clinical significance of amyloid β (Aβ) positivity on PET in cerebral amyloid angiopathy (CAA) patients. MethodsWe recruited 65 patients who met the modified Boston criteria for probable CAA.All underwent amyloid PET, MRI, APOE genotyping and neuropsychological tests, and we obtained information of CAA and ischemic cerebral small vessel disease (CSVD) MRI markers. We investigated the CAA/ischemic CSVD burden and APOE genotypes by Aβ positivity and investigated the effect of Aβ positivity on longitudinal cognitive decline. Results Among 65 CAA patients, 43(66.2 %) showed Aβ PET positivity(+). Aβ+ CAA had more lobar microbleeds(9(2,41) vs. 3(2,8), p=0.045) and a higher frequency of cortical superficial siderosis(34.9 vs. 9.1%, p=0.025), while Aβ-CAA had more lacunes(1(0,2) vs. 0(0,1), p=0.029) and a higher frequency of severe white matter hyperintensities(45.5 vs. 20.9%, p=0.040). The frequency of ε4 carriers was higher in Aβ+(57.1%) than in Aβ-CAA(18.2%) (p=0.003) while the frequency of ε2 carriers did not differ between two groups.Finally, Aβ positivity was associated with faster decline in multiple cognitive domains including language (p<0.001), visuospatial function (p<0.001), and verbal memory (p<0.001) in linear mixed effects models.3 Conclusions Our findings suggest that a significant proportion of probable CAA patients in a memory clinic are Aβ PET negative. Aβ positivity in CAA patients is associated with a distinct pattern of CSVD biomarker expression, and a worse cognitive trajectory. Aβ positivity has clinical relevance in CAA and might represent either advanced CAA or additional Alzheimer's disease neuropathologic changes.

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Amyloid positron emission tomography ([18F] florbetaben (FBB) PET) can be used to determine concomitant Alzheimer's disease (AD) in idiopathic normal pressure hydrocephalus (iNPH) patients. FBB PET scans and the tap test were performed in 31 patients with clinically suspected iNPH, and amyloid positive (iNPH/FBB+) and negative (iNPH/FBB-) groups were compared with respect to clinical characteristics. We evaluated prognostic value of FBB PET scans by analyzing the response to the tap test using a linear mixed model. We also performed a multivariable regression analysis to investigate whether amyloid PET positivity can predict the positive tap test response independent of other AD biomarkers. The results showed that the iNPH/FBB+ group (7/31, 22.6%) had a higher percentage of APOE4 carriers, lower Aβ42, higher CSF t-tau, and p-tau/Aβ42 ratio than the iNPH/FBB- group (24/31, 77.4%), while the two groups did not differ in imaging characteristics. The iNPH/FBB- group had a higher percentage of tap responders and showed a greater improvement in gait scores after the tap test than the iNPH/FBB+ group (group-tap test effect interaction, p = 0.035). A multivariable logistic regression analysis showed that amyloid positivity on PET scans (OR 0.03, p = 0.029) and CSF p-tau (OR 0.87, p = 0.044) were independently associated with the positive tap test response. Among 21 tap responders in the iNPH/FBB- group, 14 patients received shunt surgery and 12/14 (85.7%) patients showed symptom improvement. Our findings suggest that amyloid PET scans can help determine which iNPH patients will benefit from shunt surgery by discriminating concomitant AD.