Utility of Different MR Modalities in Mild Cognitive Impairment and Its Use as a Predictor of Conversion to Probable Dementia

Abstract

Mild cognitive impairment has been regarded as a pre-Alzheimer condition, but some patients do not develop dementia. The authors' objective was to determine whether findings from a combined use of H1 magnetic resonance spectroscopy (MRS), perfusion imaging (PI), and diffusion-weighted imaging (DWI) would predict conversion from amnesic mild cognitive impairment to dementia and to compare the diagnostic accuracy in discriminating patients with probable Alzheimer disease (AD), mixed dementia (MD), Lewy body dementia (LBD), pre-Alzheimer disease mild cognitive impairment (MCI), vascular MCI (VaMCI), and anxious or depression patients with cognitive impairment (DeMCI). A longitudinal cohort of 119 consecutive and incident subjects (73 women, 46 men; age 70+/-9.5 years) who fulfilled the criteria of amnesic MCI was followed for a mean period of 29 months. At baseline, a neuropsychological examination and standard blood test were performed, and different areas were examined by proton MRS, PI, and DWI. Among the group of patients considered to have AD, we also included patients with MD because these patients have a neurodegenerative component. After the follow-up period, 54 patients were considered as converted to dementia (49 with AD; 5 with LBD), 28 patients as MCI, 22 patients as DeMCI, and 15 patients as VaMCI. We found that N-acetylaspartate (NAA)/creatine (Cr) ratios in posterior cingulated gyri (PCG) predict the conversion to probable AD with a sensitivity of 82% and specificity of 72%, and NAA/Cr ratios in the left occipital cortex (LOC) had a sensitivity of 78% and specificity of 69%. When we used spectroscopy in the PCG and LOC to differentiate the types of MCI and dementias, we found significance differences in NAA/Cr, NAA/myoinositol (mI), NAA/choline (Cho), mI/NAA, and Cho/Cr ratios. The apparent diffusion coefficient (ADC) values in the right hippocampus showed differences in patients with LBD and DeMCI (P=.003), LBD with MCI (P=0.48), and LBD and VaMCI (P=.009). NAA/Cr ratios in PCG and LOC can predict the conversion from MCI to dementia with high sensitivity and specificity. MRS can differentiate AD from MCI, but cannot differentiate the types of MCI. DWI in the right hippocampus presents higher values of ADC in LBD and allows differentiating it from MCI.