N-acetylaspartate concentration in the chiasm measured by in vivo proton magnetic resonance spectroscopy.

PURPOSE: To measure the concentration of N-acetylaspartate (NAA) in the chiasm of both normal controls and patients with chiasmal optic neuritis by in vivo proton magnetic resonance spectroscopy (1H-MRS).

METHODS

Ten normal subjects (age range, 22 to 40 years; mean, 31 years; seven men and three women) and two patients with chiasmal optic neuritis were examined at the Sapporo Medical University Hospital. Localized 1H-MRS spectra of the chiasm were obtained using a whole-body 1.5-T magnetic resonance system.

RESULTS

1H-MRS spectra of the chiasm were obtained in all subjects. The level of NAA concentration in the optic chiasm was 15.73 +/- 1.43 mM (mean +/- SD) in normal subjects. In contrast, the NAA levels in the two patients with chiasmal optic neuritis were significantly lower (P < 0.001). The level of NAA in the two patients was significantly increased after improvement of visual acuity and visual fields following corticosteroid pulse therapy.

CONCLUSIONS

These results suggest that 1H-MRS enables us to estimate the concentration of NAA in the chiasm. The NAA concentration in the optic nerve measured by 1H-MRS may be a new clinical parameter to monitor the axonal damage following optic neuritis.