Clinical assessment is insensitive to the degree of cerebral involvement in amyotrophic lateral sclerosis (ALS). Regional brain concentrations N-acetylaspartylglutamate (NAA) plus myo-inositol (Ins), as measured by magnetic resonance spectroscopy, are respectively decreased and increased, suggesting that these compounds may provide a biomarker of the degree of cerebral involvement in ALS.
To test the hypothesis that the NAA/Ins ratio may provide an index of cerebral involvement in patients with ALS.
High-field (3.0-T) magnetic resonance spectroscopy was performed to determine the NAA/creatine plus phosphocreatine (NAA/Cr), NAA/choline (NAA/Cho), Ins/Cr, and NAA/Ins ratios in the motor cortex.
Seventeen patients with ALS and 15 healthy control subjects were studied.
In patients with ALS, the greatest abnormality was a 22% decrease in NAA/Ins (71% sensitivity and 93% specificity, P = .001); Ins/Cr was increased 18% (88% sensitivity and 53% specificity, P = .04), NAA/Cr was decreased 10% (88% sensitivity and 47% specificity, P = .04), and NAA/Cho was decreased 14% (53% sensitivity and 87% specificity, P = .047). Correlation of the ALS Functional Rating Scale with NAA/Ins approached statistical significance (R = 0.43, P = .07).
The NAA/Ins ratio may provide a meaningful biomarker in ALS given its optimal sensitivity and specificity profile.