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.