Cortical N-acetyl aspartate is a predictor of long-term clinical disability in multiple sclerosis.

Objective: To evaluate the prognostic value of the cortical N-acetyl aspartate to creatine ratio (NAA/Cr) in early relapsing-remitting multiple sclerosis (RRMS). Methods: Sixteen patients with newly diagnosed RRMS were studied by serial MRI and MR spectroscopic imaging (MRSI) once every 6 months for 24 months. Clinical examinations, including the expanded disability status scale (EDSS), were performed at baseline, month 24, and at year 7. Results: Baseline cortical NAA/Cr correlated inversely with EDSS at month 24 (r = -0.61, P < 0.05), and patients with EDSS >= 4 had a lower baseline cortical NAA/Cr compared to those with EDSS less than 4 (P < 0.05). Baseline cortical NAA/Cr also correlated inversely with EDSS at the 7-year follow-up (r = -0.56, P < 0.05), and patients with EDSS >= 4 had a lower baseline cortical NAA/Cr compared to those with EDSS less than 4 (P < 0.05). Baseline brain parenchymal fraction (BPF) correlated inversely with EDSS at month 24 (r = -0.61, P < 0.05), but not with EDSS at year 7. Discussion: Cortical NAA/Cr in early RRMS correlated with clinical disability after 2 and 7 years and may be used as a predictor of long-term disease outcome.