Diffusion tensor MRI and fiber tractography of cerebellar atrophy in phenytoin users.

Purpose: The usefulness of diffusion tensor magnetic resonance imaging (DT-MRI) is still in debate, and the development of clinically feasible scan protocol is encouraged. The purpose of this study was to investigate the afferent fiber system to the cerebellum in patients with phenytoin (PHT)-induced cerebellar atrophy in comparison with cerebellar atrophy of other etiologies by using DT-MRI.
Methods: Thirteen patients (M/F ratio, 7:6; mean age, 42.5 years) and age-matched normal controls (n = 8) participated in this study. The patient group consisted of epilepsy patients who had received PHT therapy (n = 9) and clinically diagnosed as having olivopontocerebellar atrophy (OPCA; n = 4). DT-MRI was performed by using diffusion weighting of b = 600 s/mm2, and fractional anisotropy (FA) and color-coded vector maps were generated. FA of the middle cerebellar peduncle (MCP), the cerebellum, and transverse pontine fibers (TPF) was measured and compared between PHT and OPCA patients.
Results: Normal subjects showed FA values of 0.81 +/- 0.07 in MCP, 0.69 +/- 0.04 in TPF, and PHT users showed FA values of 0.84 +/- 0.09 in MCP, 0.72 +/- 0.08 in TPF, and 0.21 +/- 0.04 in cerebellum. OPCA patients showed FA values of 0.39 +/- 0.11 in MCP, 0.46 +/- 0.12 in TPF, and 0.22 +/- 0.07 in cerebellum. PHT users showed a statistically significant reduction of FA only in cerebellum, whereas OPCA demonstrated significant decrease of FA in MCP, TPF, and cerebellum (one-way analysis of variance, p < 0.01). Three-dimensional reconstruction of fiber tracts demonstrated decreased volume and altered fiber integrity within the peduncles and transverse pontine fibers in the OPCA group, whereas fiber course patterns in PHT users were similar to those in controls.
Conclusions: PHT users showed normal orientation and anisotropy of MCP and TPF, whereas OPCA demonstrated impaired values, suggesting that PHT directly affects the cerebellum. DT-MRI can demonstrate detailed fiber configurations in degenerative diseases of brainstem and cerebellum and provides insight into the pathomechanisms of cerebellar atrophy.