Normal-appearing white matter in optic neuritis and multiple sclerosis: a comparative proton spectroscopy study

We investigated neurochemical abnormalities in the normal-appearing white m atter (NAWM) on MRI of patients with optic neuritis (ON) and compared them to those of patients with multiple sclerosis (MS). Patients with ON (42) we re classified into three groups according to abnormalities on brain MRI. Pa tients with MS (55) were devided in two groups: relapsing remitting MS (RRM S) and secondary progressive MS (SPMS). All patients underwent MRI of the b rain and localised proton magnetic resonance spectroscopy (MRS) of NAWM. Th e results were compared to those of 15 controls. Patients with MS had signi ficant abnormalities compared with controls and with patients with ON. Pati ents with RRMS and those with ON had comparable MRS parameters, while patie nts with SPMS had significant spectroscopic abnormalities in comparison wit h controls, but also with patients with RRMS. These changes consisted of a decrease in N-acetyl-aspartate, a neuronal marker, which may reflect axonal dysfunction and/ or loss. MRS abnormalities were detected in 14 patients w ith ON (27%). The main abnormalities consisted of a decrease in N-acetylasp artate, an increase in choline-containing compounds at long echo times, and the presence of free lipid peaks at short echo times. MRS of the NAWM on M RI may prove useful for detecting neurochemical brain abnormalities in ON n ot visible on MRI.