Diffusion tensor imaging in acute optic neuropathies: predictor of clinical outcomes.

OBJECTIVE

To evaluate directional diffusivities within the optic nerve in a first event of acute optic neuritis to determine whether decreased axial diffusivity (AD) would predict 6-month visual outcome and optic nerve integrity measures.

DESIGN

Cohort study.

SETTING

Academic multiple sclerosis center. Patients  Referred sample of 25 individuals who presented within 31 days after acute visual symptoms consistent with optic neuritis. Visits were scheduled at baseline, 2 weeks, and 1, 3, 6, and 12 months.

MAIN OUTCOME MEASURES: Visual acuity, contrast sensitivity, visual evoked potentials (VEPs), and thickness of the retinal nerve fiber layer (RNFL).

RESULTS

An incomplete 6-month visual recovery was associated with a lower baseline AD (1.50 μm(2)/ms [95% confidence interval {CI}, 1.36-1.64 μm(2)/ms for incomplete recovery vs 1.75 μm(2)/ms [95% CI, 1.67-1.83 μm(2)/ms] for complete recovery). Odds of complete recovery decreased by 53% (95% CI, 27%-70%) for every 0.1-unit decrease in baseline AD. A lower baseline AD correlated with worse 6-month visual outcomes in visual acuity (r = 0.40, P = .03), contrast sensitivity (r = 0.41, P = .02), VEP amplitude (r = 0.55, P < .01), VEP latency (r = -0.38, P = .04), and RNFL thickness (r = 0.53, P = .02). Radial diffusivity increased between months 1 and 3 to become higher in those with incomplete recovery at 12 months than in those with complete recovery (1.45 μm(2)/ms [95% CI, 1.31-1.59 μm(2)/ms] vs 1.19 μm(2)/ms [95% CI, 1.10-1.28 μm(2)/ms]).

CONCLUSIONS

Decreased AD in acute optic neuritis was associated with a worse 6-month visual outcome and correlated with VEP and RNFL measures of axon and myelin injury. Axial diffusivity may serve as a marker of axon injury in acute white matter injury.