Sheikh-Bahaei N, et al. - Experts investigated if the level of metabolites in magnetic resonance spectroscopy (MRS) was a representative marker of underlying pathological changes detected in the positron emission tomographic (PET) images among patients with Alzheimer's disease (AD). Myoinositol (mI)/creatine (Cr) exhibited significant temporal and spatial correlations with amyloid beta, while total N-acetyl (tNA) could be an indicator of early neurodegenerative changes. Both have the potential to be disease stage biomarkers, with tNA also serving as a good surrogate marker for treatment response.

Methods

• PET-guided MRS was conducted in cases of probable AD, mild cognitive impairment (MCI), and healthy controls (HC).
• Study participants were imaged by ¹¹C-Pittsburgh compound B (¹¹C-PiB) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET followed by 3T MRS.
• PET images were evaluated both visually and using standardized uptake value ratios (SUVRs).
• On PET scans, MRS voxels were placed in regions with maximum abnormality on amyloid (Aβ+) and FDG (hypometabolic) areas.
• In controls, the corresponding normal areas were selected.
• Researchers compared the ratios of total N-acetyl (tNA) group, myoinositol (mI), choline, and glutamate + glutamine over creatine (Cr) between these regions.

Results

• Aβ+ regions presented with considerably higher (p=0.02) mI/Cr and lower tNA/Cr (p=0.02).
• On the other hand, in hypometabolic areas only tNA/Cr was reduced (p=0.003).
• After adjusting for sex, age, and education, multiple regression analysis demonstrated that mI/Cr correlated solely with ¹¹C-PiB SUVR (p < 0.0001).
• Conversely, tNA/Cr exhibited a link with both PiB (p=0.0003) and ¹⁸F-FDG SUVR (p=0.006).
• Between MCI and AD, no significant variation was determined in the level of mI/Cr (p=0.28), but tNA/Cr exhibited a significant decline from HC to MCI to AD (p=0.001, p=0.04).