Fractional anisotropy values detect pyramidal tract involvement in multiple system atrophy

Area of Science:

• Neuroimaging
• Neurodegenerative diseases
• Neuropathology

Background:

• Pathological studies indicate substantial pyramidal tract involvement in multiple system atrophy (MSA), yet clinical signs are infrequent.
• Clinical presentation of pyramidal signs in MSA is often inconsistent with the observed pathological changes.

Purpose of the Study:

• To investigate fractional anisotropy (FA) values for assessing pyramidal tract involvement in MSA compared to amyotrophic lateral sclerosis (ALS) and controls.
• To compare FA values in MSA patients with and without clinical pyramidal signs or conventional MRI findings against controls.

Main Methods:

• Diffusion tensor imaging (DTI) and tractography were used to evaluate FA values.
• FA was measured in the internal capsule, corona radiata, and the entire pyramidal tract.
• The study included 20 probable MSA patients, 28 ALS patients, and 17 healthy controls.

Main Results:

• MSA patients exhibited significantly lower FA values in the pyramidal tract compared to controls, comparable to ALS patients.
• Reduced FA was observed even in early-stage MSA, in patients lacking specific MRI markers (precentral gyrus hyperintensity), and those without clinical pyramidal signs.
• FA values effectively quantified pyramidal tract degeneration in MSA, irrespective of clinical or conventional imaging evidence.

Conclusions:

• Fractional anisotropy (FA) is a sensitive marker for detecting pyramidal tract degeneration in multiple system atrophy (MSA), even in early stages.
• FA can identify pyramidal tract damage in MSA patients who lack clinical pyramidal signs or abnormal conventional MRI findings.
• The findings suggest a greater extent of pyramidal tract involvement in MSA than previously understood based on clinical and standard MRI assessments.