Assessment of brain white matter fiber bundle atrophy in patients with Friedreich ataxia

Purpose: To investigate in vivo severity and topographic distribution of brain white matter (WM) fiber bundle atrophy in patients with Friedreich ataxia, a condition characterized by an uneven involvement of brain WM, and to correlate such findings with the clinical status of the patients. Materials and Methods: The study was conducted with institutional review board approval. Written informed consent was obtained from each participant. Sixteen patients with Friedreich ataxia and 15 healthy control subjects were studied by using a 1.5-T magnetic resonance (MR) imager and 3-mm-thick diffusion-tensor images with 15 noncollinear directions. The size of WM fiber bundles was examined at a voxel level by using a recently developed method, which relies on production of anisotropy maps and nonlinear registration. Data were analyzed by using statistical parametric mapping software and an analysis of covariance model adjusted for age and sex. Results: Compared with control subjects, patients with Friedreich ataxia had WM atrophy in (a) the central portion of the medulla oblongata, (b) the dorsal upper pons, (c) the superior cerebellar peduncles, (d) the central portion of the midbrain, (e) the medial portion of the right cerebral peduncle, (f) the peridentate region, bilaterally, and (g) the optic chiasm. The severity of the neurologic deficits correlated significantly with atrophy of the peridentate WM, bilaterally, and that of the superior cerebellar peduncle decussation. Conclusion: Findings of this study show that it is feasible to obtain in vivo atrophy estimates of specific brain WM fiber bundles in patients with Friedreich ataxia and that such estimates correlate with patients' clinical status. This approach has the potential to provide new information that is likely to improve the understanding of the pathophysiology of inherited ataxias.