Cognitive impairment: assessment with brain magnetic resonance imaging and proton magnetic resonance spectroscopy

In vivo proton magnetic resonance spectroscopy is a safe and noninvasive tool that can be used to study aspects of brain chemistry and metabolism. This study was designed to evaluate its role in routine application to reveal the diagnostic reasons for cognitive impairment.

37 Alzheimer's disease patients (NINCDS-ADRDA criteria), 31 patients with subcortical ischemic vascular dementia (Chui et al. criteria), and 13 subjects with subjective cognitive impairment (DSM-IV criteria) were included in this retrospective study. Magnetic resonance images were used for atrophy rating; additionally, proton magnetic resonance spectroscopy was performed.

Significantly reduced N-acetylaspartate levels (p <.05) were found in both patients with Alzheimer's disease and patients with subcortical ischemic vascular dementia compared to the group with subjective memory complaints. The ratios of N-acetylaspartate/creatine and N-acetylaspartate/myo-inositol were significantly lower in Alzheimer's disease patients compared to patients with vascular dementia (p =.012) or patients with subjective memory impairment (p =.002). N-acetylaspartate/creatine and N-acetylaspartate/myo-inositol ratios were positively correlated to the degree of cerebral atrophy. Disoriented patients displayed a low N-acetylaspartate/creatine ratio. In contrast, we were not able to relate concurrent psychotic or behavioral symptoms to any spectroscopic parameter.

This study indicates that proton magnetic resonance spectroscopy parameters could provide additional information in differentiating between Alzheimer's disease, subcortical ischemic vascular dementia, and subjective cognitive impairment. Therefore, this method can contribute to the routine diagnosis of dementia. Psychiatric and behavioral symptoms associated with dementia or due to a major psychiatric disorder cannot be related to changes in the measured proton magnetic resonance spectroscopy parameters.