In vivo detection of beta-amyloid at the nasal cavity and other skull-base sites: a retrospective evaluation of ADNI1/GO.

Introduction: Amyloid beta (Aβ) is partially cleared from the CSF via skull base perivascular and perineural lymphatic pathways, particularly at the nasal cavity. In vivo differences in Aβ level at the nasal cavity between patients with Alzheimer's disease (AD), subjects with mild cognitive impairment (MCI) and cognitively normal (CN) individuals have not been previously assessed.

Methods: This is a retrospective evaluation of subject level data from the ADNI-1/GO database. Standardized uptake value ratio (SUVR) maximum on C-Pittsburgh compound-B (PiB)-PET was assessed at the nasal cavity on 223 scans. Exploratory ROI analysis was also performed at other skull base sites. SUVR maximum values and their differences between groups (CN, MCI, AD) were assessed. CSF Aβ levels and CSF Aβ 42/40 ratios were correlated with SUVR maximum values.

Results: 103 subjects with 223 PiB-PET scans (47 CN, 32 AD and 144 MCI) were included in the study. The SUVR maxima at the nasal cavity were significantly lower in subjects with AD [1.35 (± 0.31)] compared to CN [1.54 (± 0.30); p = 0.024] and MCI [1.49 (± 0.33); p = 0.049]. At very low CSF Aβ, less than 132 pg/ml, there was significant correlation with nasal cavity SUVR maximum. The summed averaged SUVR maximum values were significantly lower in subjects with AD [1.35 (± 0.16)] compared to CN [1.49 (± 0.17); p = 0.003] and MCI [1.40 (± 0.17); p = 0.017].

Conclusion: Patients with AD demonstrate reduced nasal cavity PiB-PET radiotracer uptake compared to MCI and CN, possibly representing reduced Aβ clearance via perineural/perivascular lymphatic pathway. Further work is necessary to elucidate the true nature of this finding.