RESUMEN
<p><b>INTRODUCTION</b>Motor neuron damage and cortical spinal tract (CST) degeneration in amyotrophic lateral sclerosis (ALS) are difficult to visualise and quantify on conventional magnetic resonance imaging (MRI).</p><p><b>CLINICAL PICTURE</b>We studied 8 ALS patients and 12 normal volunteers using diffusion tensor imaging (DTI) and fibre tractography using fibre assignment by continuous tracking (FACT) to study the fibres of the CST and the posterior thalamic radiation (PTR), a nonmotor tract.</p><p><b>OUTCOME</b>Fibre tractography was successfully performed in all normal volunteers and all patients except 1. The fibre bundles of the CST, but not the PTR, were significantly reduced (P <0.05) in patients compared to normal volunteers.</p><p><b>CONCLUSION</b>Fibre tractography can visualise axonal degeneration in the CST and may provide supplementary information about upper motor neuron disease in ALS patients.</p>