Fractional anisotropy in the posterior limb of the internal capsule and prognosis in amyotrophic lateral sclerosis.

OBJECTIVE To explore the value of diffusion tensor imaging applied to those specific cerebral white matter tracts consistently involved pathologically in amyotrophic lateral sclerosis as a source of prognostic biomarkers. DESIGN Baseline clinical assessment and 3-T diffusion tensor imaging, repeated after approximately 6 months.Tract-based spatial statistics were used to assess voxel wise correlations of just the baseline diffusion tensor imaging indices with the progression rate (change in disability score/time interval) within the corticospinal tract and corpus callosum. PATIENTS The study involved 21 patients with amyotrophic lateral sclerosis and 3 patients with primary lateral sclerosis. RESULTS Correlation was observed between fractional anisotropy and progression rate for a region of the corticospinal tract spanning the posterior limb of the internal capsule, with a left hemisphere emphasis. Posterior limb of the internal capsule fractional anisotropy showed potential to distinguish those patients with rapid progression. Axial diffusivity significantly increased in this region in a paired t test analysis of baseline and follow-up diffusion tensor imaging, in keeping with axonal damage.No correlations were noted for the corpus callosum. CONCLUSIONS Posterior limb of the internal capsule fractional anisotropy is a candidate prognostic marker in amyotrophic lateral sclerosis, with potential to identify incident cases with more rapid progression.