Disappearing corticospinal tract on routine MRI: dynamic signal evolution in primary lateral sclerosis

Area of Science:

• Neurology
• Neuroimaging
• Pathophysiology

Background:

• Primary lateral sclerosis (PLS) is a rare, adult-onset motor neuron disease.
• Corticospinal tract (CST) and motor cortex MRI findings in PLS are known but their longitudinal changes are not well understood.

Purpose of the Study:

• To describe the longitudinal evolution of MRI findings in two definite Primary Lateral Sclerosis (PLS) cases.
• To investigate the dynamic changes in corticospinal tract (CST) and motor cortex imaging markers over time.

Main Methods:

• Qualitative visual magnetic resonance imaging (MRI) scoring was used for assessment.
• Two patients with definite PLS were followed for 15 and 6 years, respectively.
• Fluid-attenuated inversion recovery (FLAIR) and susceptibility-weighted imaging (SWI) were utilized.

Main Results:

• Both patients initially showed CST hyperintensity on FLAIR.
• Despite clinical decline, serial MRIs revealed complete CST normalization (score 0/16) in both cases.
• Progressive motor cortex hypointensity on SWI, indicative of iron deposition, was observed concurrently.

Conclusions:

• A normal-appearing CST on MRI does not exclude advanced PLS.
• Progressive motor cortex hypointensity on SWI may represent a more stable imaging marker in PLS.
• Observed MRI marker dissociation suggests dynamic pathophysiological processes, possibly involving inflammation and gliotic remodeling.