Cerebral perfusion correlates of conversion to Alzheimer's disease in amnestic mild cognitive impairment

Objective: Aim of this study was to find cerebral perfusion correlates of conversion to dementia in patients with amnestic MCI. Methods: 17 healthy subjects (age = 69 ± 3, 9 females), and 23 amnestic MCI patients (age = 70 ± 6, 10 females) underwent brain MR scan and ^99mTc ECD SPECT. Conversion to AD was ascertained on average 19 ± 10 months after baseline: 9 had converted (age = 69 ± 3, 4 females), and 14 had not (age = 71 ± 8, 6 females). We processed SPECT images with SPM2 following an optimized protocol and performed a voxel-based statistical analysis comparing amnestic MCI patients converted to AD and non-converted to dementia vs controls. We assessed the effect of gray matter atrophy on the above results with SPM2 using an optimized Voxel-Based Morphometry (VBM) protocol.We compared significant hypoperfusion with significant atrophy on a voxel-byvoxel basis. Results: In comparison with normal controls, amnestic MCI patients who converted to AD showed hypoperfusion in the right parahippocampal gyrus and left inferior temporal and fusiform gyri,whereas those who did not convert showed hypoperfusion in the retrosplenial cortex, precuneus and occipital gyri, mainly on the left side.We found no overlap between significant atrophy and significant hypoperfusion regions. Conclusions: Parahippocampal and inferior temporal hypoperfusion in amnestic MCI patients appears as a correlate of conversion to AD; hypoperfusion in the retrosplenial cortex is involved in memory impairment but does not seem the key prognostic indicator of conversion to dementia.