Proton MR spectroscopy detects a relative decrease of N-acetylaspartate inthe medial temporal lobe of patients with AD

Background: The reduction of N-acetylaspartate (NAA) detected by proton MR spectroscopy (H-1-MRS) represents a robust but unspecific marker for neuron al loss or dysfunction. Objective: To apply H-1-MRS in two brain regions th at reflect the characteristic spatial distribution of neuronal loss in AD. These regions are the medial temporal lobe (MTL), which is affected early i n AD, and the primary motor and sensory cortex (central region), which is a ffected late in the disease and might serve as an intraindividual control r egion in mild to moderate disease stages. Methods: Twenty patients and 18 v olunteers underwent H-1-MRS in both brain areas. The metabolic ratios of NA A/creatine and choline/creatine were determined. Additionally, the metaboli c ratios of the MTL were divided by the ratios of the central region to ass ess the relative change in the MTL in individual subjects. All ratios were correlated with psychometric test scores. Results: A significant reduction of NAA/creatine and choline/creatine ratios was detected in the MTL of pati ents with AD. In the central region, no significant difference between the groups was found. NAA/creatine (MTL/central region) was reduced in patients with AD and showed a correlation with the Mini-Mental State Examination an d the cognitive part of the Alzheimer Disease Assessment Scale scores. Chol ine/creatine (MTL/central region) did not show a significant difference bet ween groups. Conclusion: Assessing the distribution of NAA/creatine reducti on guided by the expected neuropathologic change can improve the role of H- 1-MRS in the assessment of AD. The disease severity can be monitored by rel ative reduction of NAA/creatine in the MTL in comparison with an intraindiv idual unaffected control region.