Decreased glutamate plus glutamine in Alzheimer's disease detected in vivo with 1H-MRS at 0.5 T

Objective: To determine whether glutamate + glutamine (GLX) levels in the brain as measured in vivo with proton MRS at 0.5 tesla (T) distinguish between probable Alzheimer's disease and normal aging. Background: Glutamatergic markers had been measured previously in postmortem brain tissue. Conventional proton MRS at 1.5 T cannot reliably detect the GLX resonance in vivo. The authors developed a technique at 0.5 T that is sensitive to the GLX resonance. Methods: Metabolite ratios using creatine and phosphocreatine resonance as an internal standard were acquired from the cingulate region of 18 patients with AD and 12 healthy controls. The major resonances in the spectrum were examined: N-acetylaspartate (NAA), choline-containing compounds, myo-inositol, and GLX. The Mini-Mental State Examination (MMSE) was used to assess cognitive status. The Instrumental Activities of Daily Living Scale (Instrumental ADL) was used to assess functional status. Results: Reduced ratios of GLX(-10%, p = 0.001) and NAA (-12%, p = 0.000) were found in patients with AD. Increased ratios of myo-inositol in patients with AD approached significance (+14%). GLX ratios of patients with AD were correlated with MMSE (r = 0.61, p = 0.007) and Instrumental ADL (r = 0.59, p = 0.01) scores. The combined sensitivity of NAA and myo-inositol in correctly diagnosing AD was 78%. The addition of GLX to NAA and myo-inositol increased the sensitivity to 89%. Overall diagnostic accuracy improved from 80 to 83% with the addition of GLX. Conclusions: Glutamate + glutamine reduction may be a biologic marker for AD and may be a potential aid in the early clinical diagnosis of AD.